Methods for constructing underground borehole configurations and related solution mining methods

ABSTRACT

Disclosed are methods for solution mining of evaporite minerals, such as trona, comprising drilling an access well and at least two lateral boreholes; injecting a fluid; circulating the fluid through the lateral boreholes with a controlled fluid flow; and collecting a pregnant solution. Also disclosed are methods of solution mining that include injecting an aqueous solution into an underground trona cavity at a temperature sufficient to maintain at least a portion of the solution in the cavity in the Wegscheiderite solid phase region; removing aqueous solution from the cavity; and recovering alkaline values from the removed aqueous solution. Also disclosed are methods of solution mining that include injecting an aqueous solution into an underground trona cavity; removing aqueous solution from the cavity, wherein the temperature of the removed aqueous solution is at about the TWA point temperature; and recovering alkaline values from the removed aqueous solution.

The present application is a Continuation application of U.S. patentapplication Ser. No. 13/193,995, filed on Jul. 29, 2011, now U.S. Pat.No. 8,899,691, which is a Continuation application of U.S. patentapplication Ser. No. 12/566,446, filed on Sep. 24, 2009, now U.S. Pat.No. 8,057,765, which is a Continuation application of U.S. patentapplication Ser. No. 11/206,659, filed on Aug. 17, 2005, now U.S. Pat.No. 7,611,208, which claims priority of U.S. Provisional PatentApplication No. 60/602,371 filed Aug. 17, 2004; U.S. Provisional PatentApplication No. 60/602,372 filed Aug. 17, 2004; U.S. Provisional PatentApplication No. 60/615,941 filed Oct. 6, 2004; and U.S. ProvisionalPatent Application No. 60/669,397 filed Apr. 8, 2005, all of whichapplications are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention is directed to methods of constructing undergroundborehole configurations and to related methods of solution mining andproduction of commercial products. Underground borehole configurationsinclude configurations for water wells and storage facilities forsolids, liquids and/or gases. Mining methods of the present inventionalso relate to solution mining of soluble ore minerals and in situproduction of other ores and energy yielding resources.

BACKGROUND OF THE INVENTION

Trona is a naturally occurring sodium sesquicarbonate(Na₂CO₃.NaHCO₃.2H₂O). The Green River basin in southwestern Wyomingcontains the world's largest known deposit of trona. Reserves in Wyomingamount to approximately 140 billion tons. In the Green River Basin thereare approximately twenty-five beds of trona more than four feet thickwith intervening strata of shale. These beds are encountered at a belowsurface depth between 500 and 3000 feet.

Trona is the principle source mineral for the United States soda ashindustry and is generally produced by conventional underground miningmethods. Mined ore is hoisted to the surface and is commonly processedinto soda ash either by the ‘sesquicarbonate process’ or the‘monohydrate process.’ In the sesquicarbonate process, the processingsequence involves underground mining; crushing; dissolving raw ore inmother liquor; clarifying; filtering; recrystallizing sodiumsesquicarbonate by evaporative cooling; and converting to a mediumdensity soda ash product by calcining. The monohydrate process involvesunderground mining, crushing; calcining of raw trona ore to removecarbon dioxide and some organics to yield crude soda ash; dissolving thecrude soda ash; clarifying the resultant brine; filtering the hotsolution; removing additional organics; evaporating the solution tocrystallize sodium carbonate monohydrate; and drying and dehydratingsodium carbonate monohydrate to yield the anhydrous soda ash product.

Solution mining of trona has been proposed to minimize environmentalimpacts and reduce or eliminate the costs of underground mining,hoisting, crushing, calcining, dissolving, clarification,solid/liquid/vapor waste handling and environmental compliance. Thenumerous salt (NaCl) solution mines operating throughout the worldexemplify solution mining's potential low cost and environmental impact.Attempts to solution mine trona using vertical boreholes began soonafter the 1940's discovery of trona in the Green River Basin in Wyoming.U.S. Pat. No. 3,050,290 discloses a process for solution mining of tronathat suggests using a mining solution at a temperature of the order of100° C.-200° C. This process requires the use of recirculating asubstantial portion of the mining solution removed from the formationback through the formation to maintain high temperatures of thesolution. A bleed stream from the recirculated mining solution isconducted to a recovery process during each cycle and replaced by wateror dilute mother liquor. U.S. Pat. No. 3,119,655 discloses a process forthe recovery of soda ash from trona and recognizes that trona can berecovered by solution mining. This process includes introduction ofwater heated to about 130° C. and recovery of a solution from theunderground formation at 90° C.

These solution-mining attempts failed to mature. Instead, large-scaletraditional underground mines were developed with combined capacity inexcess of 17,000,000 tons per year. The most recent borehole tronasolution mine attempt involved connecting multiple conventionallydrilled vertical wells along the base of a preferred trona bed.Hydraulic fracturing was used to connect the wells. FMC Corp. was theprimary company attempting to develop such trona solution mining. FMCstaff published a report (E&MJ September 1985 “FMC's Newest Goal:Commercial Solution Mining Of Trona” including “Past attempts andfailures”) promoting the hydraulic fracture well connection of wellpairs as the new development that would commercialize trona solutionmining. The application of hydraulic fracturing for trona solutionmining was found to be unreliable. Fracture communication attemptsfailed in some cases and in other cases gained communication but not inthe desired manner. The fracture communication project was abandoned inthe early 1990's. Such hydraulic fracturing of trona has been proposed,claimed or discussed in numerous patents such as U.S. Pat. No. 2,847,202(Pullen); U.S. Pat. No. 2,919,909 (Rule), among others.

At the present time, trona from the Green River basin is mainly producedby conventional mining methods described above, however, as part of aunderground tailings disposal projects, operators have flooded oldworkings, dissolving the pillars and recovering the dissolved sodiumvalue. This process was pioneered by FMC and described by their staff inthe April 1999 E&MJ article “FMC's New Soda Ash Technology Is ASuccess”. The tailings disposal slurry deposits the solids in the oldunderground workings and the clarified solution dissolves some of thetrona remaining in the mine pillars. The solution is then pumped tosurface and evaporated, steam stripped to convert some of thebicarbonate to carbonate in solution, the remaining bicarbonate ions areconverted to carbonate by a lime reaction, a solid phase soda ashdecahydrate is recovered and the depleted solution is returned to theunderground tailings disposal system. The soda ash decahydrate becomesan alternative feed stock to the existing monohydrate process plantproviding the commercial soda ash products. This process is described inU.S. Pat. No. 5,283,054 issued in February 1994 to Copenhafer, Smith andNiedringhans. Individually, the process steps of this patent(evaporation to concentrate the solutions, steam stripping to convertsome of the bicarbonate to carbonate, lime process (hydroxide process)conversion of the remaining bicarbonate ions to carbonate and thedecahydrate process to recover soda ash values) are well-knownprocesses.

Directional drilling from the ground surface has been used to connectdual wells for solution mining bedded evaporite deposits and theproduction of sodium bicarbonate, potash and salt. Directional drillingis used for solution mining bedded nahcolite deposits (naturallyoccurring sodium bicarbonate) and is described in Day, R. 1994 “WhiteRiver Nahcolite Solution Mine,” Society for Mining, Metallurgy, andExploration Meeting and Exhibit, February 1994, Albuquerque, N. Mex.Development of nahcolite solution mining cavities by using directionallydrilled horizontal holes and vertical drill wells is described in U.S.Pat. No. 4,815,790, issued in 1989 to E. C. Rosar and R. Day, entitledNahcolite Solution Mining Process and in United States StatutoryInvention Registration No. H614, entitled “Method to Connect Drill HolesUtilizing Signaling Devices” to Robert Norman. The use of directionaldrilling for trona solution mining is described in U.S. PatentApplication Publication No. US 2003/0029617 entitled “Application,Method and System For Single Well Solution Mining” by N. Brown and K.Nesselrode.

However, most trona deposits occur in narrow layered beds where theresource is disposed in beds that extend primarily horizontally withdiscrete boundaries of nonsoluble or nonevaporite rock disposed inbetween the beds. This bed configuration is costly to mine byconventional mining methods but this remains the dominant trona miningmethod. The practice of solution mining pillars does not materiallyimprove the overall high soda ash production cost due to the high costinitial trona mining. There has been no known experimental or commercialactivity to apply the directional drilling solution-mining methods knownto the art.

Trona and nahcolite are the principle source minerals for the UnitedStates sodium bicarbonate industry. Sodium bicarbonate is produced bywater dissolution and carbonation of either mechanically mined trona oreor the soda ash produced from that ore. Sodium bicarbonate is alsoproduced by solution mining nahcolite, the naturally occurring form ofsodium bicarbonate. Nahcolite solution mining utilizes directionallydrilled boreholes and a hot aqueous solution comprised of dissolved sodaash, sodium bicarbonate and salt. In either case, the sodium bicarbonateis produced by cooling or a combination of cooling and evaporativecrystallization.

Uranium mining is often by in situ leach methods (also known as solutionmining). Uranium deposits, suitable for solution mining, generally occurin permeable sandstones, confined above and below by impermeable strataand below the water table. A wellfield design is typically a grid withalternating production and injection wells drilled vertically fromsurface. The well grid is typically drilled such that there is aborehole, drilled from the surface, in a center position. Fluid isinjected into the permeable strata from this center borehole. Rangedaround the center borehole are a number of boreholes, also drilled fromthe surface, from which fluid that has passed through the permeablestrata is collected and recovered. This fluid contains dissolved uraniumminerals that may then be recovered.

However, there remains a need in the art for improved methods ofsolution mining for evaporite minerals, in particular trona, andimproved methods of solution mining non-evaporite soluble ores such asthose containing uranium, and improved methods of producing coal, tarsands, heavy oil and oil shale. There remains a need in the art forsolution mining methods that enhance resource recovery from evaporitemineral or ore beds, allow for recovery of a solvent that is rich indesired dissolved minerals and lean in undesired dissolved mineralsleading to more cost effective winning of commercial products from thesolvent, and reduced environmental impacts compared to conventionalunderground mining. There also remains a need in the art for undergroundconfigurations which allow for efficient storage and/or disposal ofsolids, gases and/or liquids; water wells; and containmentsystems/recovery systems for plumes of underground contaminants as wellas for production of shale oil, heavy oils, tar sands and enhancedrecovery from depleted conventional oil fields.

SUMMARY OF THE INVENTION

One embodiment of the present invention is a method for solution miningof an evaporite mineral. The method includes drilling at least oneaccess well accessing an evaporite mineral formation. The method furtherincludes drilling at least two lateral boreholes, wherein the lateralboreholes communicate with each other and at least one of the lateralboreholes is connected with the access well. A fluid is injected intothe access well and the fluid is circulated through the access well andthe two lateral boreholes, wherein substantially equal or controlledfluid flow is maintained between the lateral boreholes. A pregnantsolution containing the dissolved evaporite mineral is collected. Theaccess well can either include a single access well or two or moreaccess wells. In the embodiment where there are two access wells, thetwo lateral boreholes can be connected to the access wells at a single,multiply connected point. In further alternative embodiments, thelateral boreholes can include 3, 4, 5 or 6 lateral boreholes. Further,the ratio of lateral boreholes to access wells can be greater than orequal to 1:1, 2:1, 3:1 or 4:1.

The lateral boreholes can be disposed substantially vertically withrespect to each other or substantially horizontally with respect to eachother.

In a further embodiment, the mining configuration can include a firstand second access well, wherein fluid is injected into the first accesswell and the step of collecting a pregnant solution includes collectingthe solution from the second access well.

The access well can also include tubing that is inserted into the accesswell. In this embodiment, the access well can also include a packer.Further, the fluid can exit the tubing at the shoe of the access well orit can exit the tubing within a lateral borehole. In this embodiment,the step of injecting a fluid into the access well can include injectingthe fluid from more than one tubing inserted into the access well.

The step of collecting a pregnant solution can include collecting thepregnant solution at the shoe of the well. Further, the step ofcollecting can include collecting a pregnant solution with at least onetubing placed within an access well. The access well can be cased andcemented for at least a part of the length of the borehole.

The lateral boreholes can be created by a method that includes drillinga first lateral borehole in a first direction having a forward end on afirst plane; reciprocating the drill from the forward end of the firstlateral borehole to expand the first lateral borehole to include thesecond plane; and drilling a second lateral borehole in the secondplane.

The step of circulating a fluid can include flowing the fluid throughthe lateral boreholes in parallel, and can also include flowing thefluid through the lateral boreholes serially. In the case of a serialfluid flow, at lease one plug can be placed in the lateral borehole. Thelateral boreholes can be between about 25 feet and 750 feet in distancefrom each other.

The evaporite mineral can be selected from halite, carbonate, nitrate,iodate, borate, sulfate, and phosphate. In other embodiments, theevaporite mineral can be selected from trona, nahcolite, halite, potash,borax, mirabuiulite, sylvite, carnalite, kalinite, nitire, langbeinite,polyhalite, schoenite, thenardite, gaylussite, pirssonite, andWegscheiderite. In a preferred embodiment, the evaporite mineral istrona.

The fluid in the method can be a solvent, and the solvent can includespecies selected from carbonic acid, sodium carbonate, sodium hydroxideand calcium hydroxide. Additionally, the solvent can be heated, such asto be between about 20° C. and about 110° C.

The method can further include placing an artificial leach barrierwithin at least one lateral borehole to control the leach rate anddirection of the evaporite minerals from within the borehole. Further,the method can include drilling at least one of the lateral boreholessuch that a natural barrier controls the leach rate in the direction ofthe evaporite minerals from within the borehole. In this embodiment, thenatural barrier can lie between the two lateral boreholes. Further, inthis embodiment, the two lateral boreholes can be disposed substantiallyvertically with respect to each other, and the upper lateral boreholecan be substantially completely solution mined before the lower lateralborehole is substantially completely solution mined. Further, thenatural barrier can either be an interbed natural barrier or an intrabednatural barrier.

A further embodiment of the invention includes a method for solutionmining of an evaporite mineral. This method includes drilling at leastone access well accessing an evaporite mineral formation and drilling atleast two lateral boreholes, wherein the lateral boreholes communicatewith each other and at least one of the lateral boreholes is connectedto the access well. The method further included injecting a fluid intothe access well and circulating the fluid through the access well andthe two lateral boreholes in a serpentine flow pattern. The methodfurther includes collecting a pregnant solution containing at least onedissolved evaporite mineral.

The access well can either include a single access well or two or moreaccess wells. In the embodiment where there are two access wells, thetwo lateral boreholes can be connected to the access wells at a single,multiply connected point. In further alternative embodiments, thelateral boreholes can include 3, 4, 5 or 6 lateral boreholes. Further,the ratio of lateral boreholes to access wells can be greater than orequal to 1:1, 2:1, 3:1 or 4:1.

The lateral boreholes can be disposed substantially vertically withrespect to each other or substantially horizontally with respect to eachother.

In a further embodiment, the mining configuration can include a firstand second access well, wherein fluid is injected into the first accesswell and the step of collecting a pregnant solution includes collectingthe solution from the second access well.

The access well can also include tubing that is inserted into the accesswell. In this embodiment, the access well can also include a packer.Further, the fluid can exit the tubing at the shoe of the access well orit can exit the tubing within a lateral borehole. In this embodiment,the step of injecting a fluid into the access well can include injectingthe fluid from more than one tubing inserted into the access well.

The step of collecting a pregnant solution can include collecting thepregnant solution at the shoe of the well. Further, the step ofcollecting can include collecting a pregnant solution with at least onetubing placed within an access well. The access well can be cased andcemented for at least a part of the length of the borehole.

The lateral boreholes can be created by a method that includes drillinga first lateral borehole in a first direction having a forward end on afirst plane; reciprocating the drill from the forward end of the firstlateral borehole to expand the first lateral borehole to include thesecond plane; and drilling a second lateral borehole in the secondplane.

The step of circulating a fluid can include flowing the fluid throughthe lateral boreholes in parallel, and can also include flowing thefluid through the lateral boreholes serially. In the case of a serialfluid flow, at lease one plug can be placed in the lateral borehole. Thelateral boreholes can be between about 25 feet and 750 feet in distancefrom each other.

The evaporite mineral can be selected from halite, carbonate, nitrate,iodate, borate, sulfate, and phosphate. In other embodiments, theevaporite mineral can be selected from trona, nahcolite, halite, potash,borax, mirabuiulite, sylvite, carnalite, kalinite, nitire, langbeinite,polyhalite, schoenite, thenardite, gaylussite, pirssonite, andWegscheiderite. In a preferred embodiment, the evaporite mineral istrona.

The fluid in the method can be a solvent, and the solvent can includespecies selected from carbonic acid, sodium carbonate, sodium hydroxideand calcium hydroxide. Additionally, the solvent can be heated, such asto be between about 20° C. and about 110° C.

The method can further include placing an artificial leach barrierwithin at least one lateral borehole to control the leach rate anddirection of the evaporite minerals from within the borehole. Further,the method can include drilling at least one of the lateral boreholessuch that a natural barrier controls the leach rate in the direction ofthe evaporite minerals from within the borehole. In this embodiment, thenatural barrier can lie between the two lateral boreholes. Further, inthis embodiment, the two lateral boreholes can be disposed substantiallyvertically with respect to each other, and the upper lateral boreholecan be substantially completely solution mined before the lower lateralborehole is substantially completely solution mined. Further, thenatural barrier can either be an interbed natural barrier or an intrabednatural barrier.

A further embodiment of the present invention includes a method forsolution mining of an evaporite mineral that includes drilling at leastone access well into an evaporite mineral formation and drilling a firstand second lateral borehole into the formation that communicate witheach other, wherein at least one of the lateral boreholes is connectedto the access well. The method further includes injecting a fluid intothe access well, circulating it through the first lateral borehole toproduce a first pregnant solution containing a dissolved evaporitemineral to produce a first cavity, and collecting the first pregnantsolution. The method further includes circulating a fluid through thesecond lateral borehole to produce a second pregnant solution containinga dissolved evaporite mineral to produce a second cavity, and collectingthe second pregnant solution. In this embodiment, the step ofcirculating the fluid to the second lateral borehole can be initiatedafter the step of circulating the fluid through the first lateralborehole, when the first lateral borehole is below the second lateralborehole. In this embodiment, a barrier between the first cavity and thesecond borehole can collapse to open a communication between the firstcavity and the second borehole.

A further embodiment of the present invention, includes a method forsolution mining of an evaporite mineral that includes drilling first andsecond access wells extending into an evaporite mineral formation anddrilling first and second substantially parallel lateral boreholes,wherein second ends of the lateral boreholes communicate and wherein thefirst end of the first lateral borehole communicates with the firstaccess well and the first end of the second lateral boreholecommunicates with the second access well. The method further includesinjecting a fluid into the first access well and collecting a pregnantsolution containing a dissolved evaporite mineral from the second accesswell. This embodiment can also include injecting a fluid into a secondwell and collecting a pregnant solution containing dissolved evaporiteminerals from the first access well. In this embodiment, the firstlateral borehole can contain at least one first access tubing and thesecond lateral borehole can contain at least one second access tubing.This embodiment further comprises injecting a fluid into the firstaccess tubing and collecting a pregnant solution containing a dissolvedevaporite mineral from the second access well. This embodiment can alsoinclude injecting a fluid into a second access tubing and collecting apregnant solution containing a dissolved evaporite mineral from thefirst access tubing. In further embodiments of the invention, thelateral boreholes can communicate via first intermediate positions oneach lateral borehole between the first and second ends of each lateralborehole. Further, the lateral boreholes can also communicate via secondintermediate positions on each lateral borehole between the first andsecond ends of each lateral borehole.

A further embodiment of the present invention includes a method forsolution mining of an evaporite mineral that includes drilling at leasttwo access wells extending into an evaporite mineral formation anddrilling a first array of at least two substantially parallel lateralboreholes. The method further includes drilling a second array of atleast two substantially parallel lateral boreholes. In this embodiment,the boreholes in the first array are not parallel with the boreholes inthe second array and the boreholes in the first and second arrayscommunicate with at least one borehole in the other array or with anaccess well. The method further includes injecting a fluid into at leastone of the access wells and collecting a pregnant solution containing adissolved evaporite mineral from at least one of the access wells. Thisembodiment can further include drilling a third array of at least twosubstantially parallel lateral boreholes wherein the boreholes in eachof the arrays are not parallel with the boreholes in any other array andwherein the boreholes in the first, second and third arrays communicatewith at least one borehole in another array or with an access well.

A further embodiment of the present invention is a method for solutionmining of an ore mineral formation. The method includes drilling atleast one access well accessing the ore mineral formation and drillingat least two lateral boreholes, each containing a first end connected tothe access well and a second end not in borehole communication with theaccess well or another lateral borehole. The method includes injectingthe fluid into the access well causing fluid flow within the ore mineralformation and collecting a pregnant solution containing a recovered oremineral from at least one lateral borehole. In a preferred embodiment,the ore mineral can include uranium. In a further embodiment, at least aportion of the lateral boreholes are substantially parallel to eachother. In a still further embodiment, at least a portion of the lateralboreholes and the access well are substantially parallel to each other.Alternatively, at least a portion of the lateral boreholes in the accesswell can be drilled such that a substantial portion of the boreholes aresubstantially perpendicular with respect to the ground surface. In thisembodiment, at least one access well can comprise a single access well.Further, the two lateral boreholes can be connected to the access wellat a single multiply connected point. The lateral boreholes can includeat least 3, at least 4, at least 5, or at least 6 lateral boreholes. Thestep of injecting a fluid into the access well can include injecting thefluid into at least one tubing inserted into the access well. The stepof collecting a pregnant solution containing a dissolved ore mineral caninclude collecting the solution at the shoe of the well. The step ofcollecting a pregnant solution can include collecting the solution withat least one tubing placed within the access well. The communicatinglateral boreholes can be created by a method that includes drilling afirst lateral borehole in a first direction having a forward end on afirst plane. The method further includes reciprocating the drill fromthe forward end of the first lateral borehole to expand the firstlateral borehole to include a second plane, and drilling a secondlateral borehole in the second plane. The fluid used in this method caninclude a solvent.

A further embodiment of the present invention includes the method ofconstructing an underground configuration that includes drilling atleast one access well and drilling at least two lateral boreholes. Thetwo lateral boreholes communicate with each other and at least one ofthe lateral boreholes is connected to the access well. Further, theunderground configuration allows for controlled fluid flow through thelateral boreholes. The underground configuration can be a water well, anevaporite ore mine, an oil shale mine, a tar sand mine, or a coal mine.Further, the underground configuration can be a containment barrier forunderground contaminants. The underground can also be a subterraneanstorage facility such as a storage facility for a gas such as naturalgas or for a liquid.

A further embodiment of the present invention is a method of solutionmining of trona. The method includes injecting an aqueous solution intoan underground cavity comprising trona to dissolve the trona. Theinjected aqueous solution comprises condensed steam produced by theevaporation of water from a solution to produce a sodium product.Further, the injected aqueous solution is at a temperature sufficient tomaintain at least a portion of the solution in the cavity in theWegscheiderite solid phase region. The method further includes removingaqueous solution from the cavity and recovering alkaline values from theremoved aqueous solution. The temperature of the removed aqueoussolution can be within the Wegscheiderite solid phase region, or it canbe about 90° C., about 120° C., about 150° C., about 180° C., about 210°C., or about 240° C. In addition, the temperature of the removed aqueoussolution can be at about the TWA point temperature. The removed aqueoussolution can also include sodium bicarbonate and sodium carbonate atconcentrations that are greater than about 75% of their maximumsolubility, greater than about 80% of maximum solubility, greater thanabout 85% of maximum solubility, greater than about 90% of maximumsolubility, greater than about 95% of maximum solubility, or greaterthan about 99% of maximum solubility. Further, the temperature of theremoved aqueous solution can be in the range of about 115° C. to about120° C., from about 110° C. to about 145° C., from about 105° C. toabout 170° C., from about 100° C. to about 190° C., or from about 90° C.to about 240° C.

In a further embodiment, the sodium product can be selected from sodiumsesquicarbonate, sodium bicarbonate, sodium carbonate monohydrate andanhydrous sodium carbonate. The step of recovering can also compriserecovering sodium carbonate monohydrate by evaporating water from theremoved aqueous solution to produce steam and condensing the steam. Inthis embodiment, the condensed steam in the aqueous solution can be thesteam condensed by the step of recovering.

The removed solution can be enriched in sodium bicarbonate and sodiumcarbonate. Further, the removed solution can be treated to form sodiumbicarbonate, sodium sesquicarbonate, sodium carbonate monohydrate oranhydrous sodium carbonate. In a preferred embodiment, the removedsolution is treated to form sodium bicarbonate by carbonating theremoved solution. Further, the removed solution can be treated to formsodium sesquicarbonate.

The step of treating can include a step selected from cooling,evaporative crystallization and combinations thereof. The method canalso include recovering sodium carbonate monohydrate from the removedsolution. In this embodiment, the process can further include a stepprior to recovering sodium carbonate monohydrate that is selected fromfortification, steam stripping, evaporation, the hydroxide process andsodium carbonate decahydrate process. The process of this embodiment canalso include introducing Ca(OH)₂ to the aqueous solution, wherebycalcium carbonate is formed and settles from the aqueous solution in thecavity. Alternative, Ca(OH)₂ can be introduced to the removed aqueoussolution, whereby calcium carbonate is formed and settles from theaqueous solution. In this embodiment, the process can further includeintroducing the calcium carbonate into an underground cavity.

A further embodiment of the present invention includes a method ofsolution mining of trona. The method includes injecting an aqueoussolution into an underground cavity that comprises trona to dissolve thetrona. The process further includes removing aqueous solution from thecavity, wherein the temperature aqueous solution is at about the TWApoint temperature. The process further includes recovering alkalinevalues from the removed aqueous solution.

In this embodiment, sodium bicarbonate and sodium carbonateconcentrations in the removed aqueous solution can be at greater thanabout 75%, about 80%, about 85%, about 90%, about 95%, or about 99% ofthe maximum solubility. Further, the temperature of the removed aqueoussolution can be in the range of about 115° C. to about 120° C., fromabout 110° C. to about 145° C., from about 105° C. to about 170° C.,from about 100° C. to about 190° C., from about 90° C. to about 240° C.

Further, the aqueous solution can comprise condensed steam produced byevaporation of water from the solution to produce sodium products. Inthis embodiment, the sodium products can be selected from sodiumsesquicarbonate, sodium bicarbonate, sodium carbonate monohydrate andanhydrous sodium carbonate. Further, in this embodiment, the step ofrecovering can include recovering sodium carbonate monohydrate byevaporating water from the removed aqueous solution to produce steam andcondensing steam. Further, the condensed steam in the aqueous solutioncan be the steam condensed by the step of recovering.

In further embodiments, the removed solution can be enriched in sodiumbicarbonate and sodium carbonate. Further, the removed solution can betreated to form sodium bicarbonate, sodium sesquicarbonate, sodiumcarbonate monohydrate or anhydrous sodium carbonate. In particular, theremoved solution can be treated to form sodium bicarbonate bycarbonating the removed solution. Alternatively, the removed solutioncan be treated to form sodium sesquicarbonate. The step of treating caninclude a step selected from the group consisting of cooling,evaporative crystallization and combinations thereof. Sodium carbonatemonohydrate can be recovered from the removed solution and prior torecovering sodium carbonate monohydrate, the solution can be treated bya step selected from fortification, steam stripping, evaporation, thehydroxide process, and the sodium carbonate decahydrate process.

The process can further include introducing Ca(OH)₂ to the aqueoussolution whereby calcium carbonate is formed and settles from theaqueous solution in the cavity. Alternatively, Ca(OH)₂ can be introducedto the removed aqueous solution whereby calcium carbonate is formed andsettles from the aqueous solution. In this embodiment, the calciumcarbonate can be introduced into an underground cavity.

In further embodiments, during the dissolution of trona, Wegscheideriteand/or nahcolite are precipitated from the mining solution in thecavity. In this embodiment, the method is conducted until the cavitybecomes effectively depleted of trona. This process further includesinjecting an aqueous solution into the cavity comprising precipitatedWegscheiderite and/or nahcolite to dissolve these minerals. The aqueoussolution is removed from the cavity and alkaline values are recoveredfrom the removed aqueous solution. In this embodiment, the temperatureof the removed aqueous solution can be above the temperature at whichsodium decahydrate can exist. Alternatively, the temperature of theremoved aqueous solution can be within the Wegscheiderite solid phaseregion. Further, the temperature of the removed aqueous solution can beabove about 30° C. Alternatively, the temperature of the removed aqueoussolution can be between about 90° C. and about 150° C.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an underground configuration of the present inventionhaving one access well and two lateral boreholes.

FIG. 2 illustrates an underground configuration of the present inventionhaving one access well and four lateral boreholes.

FIG. 3 illustrates an underground configuration of the present inventionhaving one access well and five lateral boreholes designed for parallelflow within the lateral boreholes.

FIG. 4 illustrates an underground configuration of the present inventionhaving one access well and five lateral boreholes designed for series orserpentine flow within the lateral boreholes.

FIG. 5 illustrates an underground configuration of the present inventionhaving two access wells and five lateral boreholes.

FIG. 6 illustrates an underground configuration of the present inventionhaving six access wells and multiple lateral boreholes.

FIG. 7 illustrates an underground configuration of the present inventionhaving two access wells and two lateral boreholes.

FIG. 8 illustrates an underground configuration of the present inventionhaving two access wells and five lateral boreholes.

FIG. 9 illustrates an underground configuration of the present inventionhaving two access wells and multiple lateral boreholes.

FIG. 10 illustrates an underground configuration of the presentinvention having two access wells and multiple lateral boreholes.

FIG. 11 illustrates an underground configuration of the presentinvention having two access wells and multiple lateral boreholes.

FIG. 12 illustrates an underground configuration of the presentinvention having two access wells and multiple lateral boreholes.

FIG. 13 illustrates an underground configuration of the presentinvention having two access wells and multiple lateral boreholes.

FIG. 14 is the solubility diagram for the Na₂CO₃—NaHCO₃ system.

FIG. 15 illustrates various configurations for processing miningsolution from the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention generally relates to methods of constructingunderground borehole configurations and related commercialopportunities. More particularly, the present invention relates toconstructing underground borehole configurations, solution mining ofsoluble ores, recovery of underground resources of water, undergroundcontaminate cleanup or containment, and in situ production of oil shale,coal, heavy oil and otherwise depleted conventional oil. The presentinvention, more specifically, provides a process to optimize thesolution mining of trona using both improved methods to constructunderground borehole configurations and improved methods to dissolve theore and produce commercial products.

This invention teaches the construction of improved boreholeconfigurations including efficiently drilled multiple branched lateralsand methods to favorably direct the flow of solutions and control thedissolution in the multiple branched borehole system to cause thedevelopment of highly productive solution mined cavity and process.

This invention further teaches the improved means to recover highlyconcentrated solutions that are enriched in CO₃ and depleted in lessdesirable HCO₃.

Over the years much has been made of incongruent and congruentdissolving of trona in aqueous solutions. U.S. Pat. No. 5,283,054provides an example of congruent and incongruent concepts common in theindustry. Such concepts are not true. Trona's crystal structure isunique. While trona contains the building blocks to make soda ash andsodium bicarbonate, solid phase soda ash and sodium bicarbonate do notexist in trona.

Trona does not leach—it dissolves. When it dissolves, the resultingsolution contains sodium ions, carbonate ions, bicarbonate ions, andwater. The dissolution process progresses until the solution issaturated. In the case of trona dissolution in water at temperatures ofthe nahcolite solid phase region, the sodium bicarbonate related ionsbecome saturated before the soda ash related ions. In this case, tronadissolution continues until both the soda ash and bicarbonate relatedions are saturated. This is the condition commonly referred to as being“double saturated” in the industry. In reaching the double saturatedcondition, excess sodium bicarbonate in solution supersaturates and mayprecipitate. When precipitating, solid phase sodium bicarbonate mayoccur at the trona dissolution surface as experienced in the lab andsmall-scale trona dissolution tests. This type of precipitation need notbe the case in commercial trona solution mining where conditions can becontrolled to cause localized higher supersaturation and precipitationin areas remote from the most productive trona dissolution areas. Suchsodium bicarbonate precipitation within the cavity occurs as the tronacontinues to dissolve and the soda ash related ions continue to increasein concentration. This process results in solutions that areconcentrated with the soda ash related ions and depleted in the sodiumbicarbonate related ions. Such solutions are preferred in the industryfor the production of soda ash. In the case of trona dissolution inwater at temperatures within the Wegscheiderite solid phase region, in aprocess similar to that described above, Wegscheiderite can precipitateas trona dissolves. Also in a similar manner, in the case ofWegscheiderite dissolving in water at temperatures of the Wegscheideritesolid phase region, nahcolite can precipitate as the Wegscheideritedissolves.

A second beneficial precipitation of Wegscheiderite and sodiumbicarbonate can occur when the cavity contacts bedded salt (NaCl). Saltdissolution rapidly causes high localized Wegscheiderite and sodiumbicarbonate supersaturation and precipitation at the contact of thesolution and salt. Experience shows that the resulting sodiumbicarbonate precipitation occurs at the face of the exposed salt. Thiseffect (1) slows the salt dissolution rate and (2) removes lessdesirable Wegscheiderite and sodium bicarbonate from the solution in apreferred location that enhances the commercial dissolution of the tronaore.

Trona dissolves instead of preferentially leaching various portions ofthe trona. At 40° C., water dissolving trona in the sodium bicarbonatesolid phase region of FIG. 14 becomes sodium bicarbonate saturated atPoint A′. As trona dissolution continues, it causes the solutionchemistry to move along the constant 40° C. temperature line toward thetrona solid phase region until becoming double saturated at point D. Atthis point, trona dissolution stops as both the soda ash related ionsand sodium bicarbonate related ions are at saturation with trona in thesolid phase. The phase diagram demonstrates that heating the ore cavitywhile dissolving trona in the sodium bicarbonate solid phase region incontact with the trona solid phase region increases the concentration ofthe less desirable sodium bicarbonate but could even cause the desiredsoda ash concentration to decline. One aspect of the present inventionuses an elevated temperature dissolution process to dissolve trona whilein the Wegscheiderite solid phase region of the phase diagram to gain ahighly concentrated solution that, relative to the composition of trona,is rich in the desirable soda ash and depleted in respect to sodiumbicarbonate. A preferred result is the recovery of solution thatapproaches the temperature and composition of the triple pointidentified as TWA on the phase diagram in FIG. 14. Thus, the TWA pointrefers to a solution in which Trona, Wegscheiderite, and Anhydroussodium carbonate coexist. The TWA point refers to a point in theWegscheiderite solid phase region where sodium carbonate and sodiumbicarbonate are at about maximum solubility. This phase diagram showsthe TWA point at about 115° C. Other published phase diagrams identifythe TWA point at 122° C. Solvent impurities such as salt will lower thetemperature and composition of the TWA point.

Recovered trona mining solutions approaching the concentration andnature of point TWA on the phase diagram are uniquely suited for theeconomic production of either or both sodium bicarbonate and sodiumsesquicarbonate. Cooling or a combination of cooling and evaporativecrystallization of the TWA solution produces sodium sesquicarbonate.Carbonating the TWA solution by addition of carbon dioxide to thesolution before either cooling and/or evaporative crystallizationproduces sodium bicarbonate. The sesquicarbonate and bicarbonateproduction can also be accomplished in series as well as in parallel. Inany case, the soda ash values remaining in solution following removal ofthe solid phase sodium sesquicarbonate and sodium bicarbonate products,can be recovered using well-known processes such as the monohydrate sodaash process. The sodium sesquicarbonate and sodium bicarbonate depletedsolutions can directly feed the monohydrate crystallizers or bepretreated using the well-known fortification, steam stripping,decahydrate process (cooling a sodium carbonate solution to betweenabout 5° C. and about 25° C. to precipitate sodium carbonatedecahydrate) and hydroxide process (described below). In any case, themonohydrate process provides preheated water (condensed steam) forinjection to the cavity creating a highly energy efficient closed loopsystem.

As noted, during the solution mining of trona in accordance with theinvention, the mining solution, relative to the composition of trona, isrich in desirable soda ash and depleted in respect to sodiumbicarbonate. Since the solution is saturated with nahcolite orWegscheiderite, as more trona is dissolved, the sodium bicarbonate ispreferentially removed in the form of Wegscheiderite or nahcolitedepending on the solid phase region of the system. Thus, during themining of the trona resource, a significant amount of Wegscheiderite ornahcolite can be produced in the mining cavity. As mining progresses,the mining cavity becomes effectively depleted of trona, either by themining face reaching another mineral such as shale or by mud productionthat covers the cavity floors and sloped walls, blinding the tronasurfaces from the mining solution. At that point, fresh mining solutionwill contact the significant amount of precipitated Wegscheiderite andnahcolite produced by the trona mining. This process further includescontinued solution mining at temperatures of the Wegscheiderite ornahcolite solid phase regions, recovering additional sodium values fromthe cavity using the processes and producing the products in a mannersimilar to those of this invention for the TWA solutions from a tronadominated solution mining system. A preferred recovery temperature forthis phase of mining is at about the temperature of the WTN(Wegscheiderite-Trona-Nahcolite) triple point where all minerals cancoexist in solid phase. In the pure system depicted by the phase diagramFIG. 14, this preferred recovered solution would be about 90° C., 17%soda ash and 10% sodium bicarbonate.

The present invention also teaches more cost effective methods of usinglime in the process or cavity, if needed or desired, including thedisposal of lime process waste in the cavities to reduce the cost andenvironmental impacts.

The improved borehole configuration of the present invention optimizestrona solution mining by cost-effectively increasing the borehole lengthand dissolution surface available per well, optimizing boreholepositioning within a single bed or in a multiple bed system, controllingsolution flow patterns within the borehole system and achieving highlyconcentrated solutions.

The present invention relates to improved borehole construction, therecovery of more concentrated trona solution mining solutions and limeprocess improvements for the production of sodium products. Included inthe patent is the previously undiscovered use of these inventions incombination with well known sodium mineral processing and production ofsodium products including without limitation—fortification, steamstripping, carbonation, sodium sesquicarbonate process, sodium carbonateprocess, sodium decahydrate process, sodium monohydrate process,hydroxide process, carbonic acid, etc.

The methods of the present invention provide for improved solutionmining of both evaporite minerals, such as trona, and soluble oreminerals, such as uranophane. The methods of the present inventionprovide for more economically efficient solution mining. Benefitsinclude reduced environmental impacts, enhanced resource recovery, moreefficient solution mining of evaporite beds, reduced drilling costs, andrecovered solutions rich in desired dissolved minerals and lean inundesired dissolved minerals, leading to winning of commercial productsfrom these solutions. The methods of the present invention also providefor improved underground configurations for more efficient storageand/or disposal of gases and/or liquids; underground configurations forwater wells; and containment and/or recovery systems for plumes ofunderground contaminants.

In a first embodiment, the present invention includes a method forsolution mining of an evaporite mineral which includes drilling at leastone access well accessing an evaporate mineral formation and drilling atleast two lateral boreholes, wherein the lateral boreholes communicatewith each other and wherein at least one of the lateral boreholes isconnected to the access well. The method also includes injecting a fluidinto the access well and circulating the fluid through the access welland the lateral boreholes wherein controlled fluid flow is maintainedbetween at least two lateral boreholes. Finally, the method includescollecting a pregnant solution containing a dissolved evaporite mineral.

The term solution mining refers to the dissolution and recovery ofminerals from an underground mineral deposit generally using wellsdrilled from the ground surface. Water-soluble minerals that aresusceptible to solution mining techniques include evaporite minerals.Evaporite minerals include all minerals that were precipitated fromsolutions concentrated by evaporation of solvents. Evaporite mineralssusceptible to solution mining by methods of the present inventioninclude all evaporite minerals. Preferred evaporite minerals includetrona, nahcolite, halite, potash, borax, mirabiulite, sylvite,carnallite, kalinite, soda nitire, nitire, langbeinite, polyhalite,schoenite, thenardite, gaylussite, pirssonite, Wegscheiderite, and otherevaporites in the halite, carbonate, nitrate, iodate, borate, sulfate,and phosphate classes. Non-evaporite soluble minerals are alsosusceptible to solution mining using methods of the present invention.Such non-evaporite soluble minerals may be included in permeableformations such as sandstones. Such non-evaporite soluble mineralsinclude uranophane, uraninite, chalcopyrite, chalcocite, galena,cuprite, and zincite. A preferred soluble mineral is trona.

Appropriate evaporite mineral formations for the solution mining methodsof the present invention include classifications such as massive,bedded, or matrix. A massive ore example is salt in huge pure domes. Abedded ore example is trona beds sandwiched by oil shale. A matrix oreexample is nodular and crystalline nahcolite contained in a nearlyimpervious oil shale formation. All may be solution mined using thepresent invention.

Drilling according to methods of the present invention includes the useof all types of drills known in the art, including down-hole turbinemotor drilling units. Preferably, use of the drill is combined with useof an attached Measurement While Drilling (MWD) tool that usesmechanical and electronic techniques to allow drilling in a controlleddirectional manner. Another function of the MWD is to provide nearlyreal-time geophysical data to the driller on the surface who is steeringthe drilling assembly. The combination of tools used to drill and directthe drilling is commonly called the drilling assembly.

The first step of the method is drilling at least one access wellaccessing a soluble mineral formation. An access well includes aborehole that is drilled from the ground surface into a solubleevaporite or non-evaporite mineral ore body. Generally, an access wellis not intended for solution mining in and of itself. Rather, an accesswell is generally used as a conduit for which fluid is conducted intoand out from the lateral boreholes or the cavities that result fromsolution mining these lateral boreholes. The access well will typicallybe cased and cemented substantially from surface to the solubleevaporite or non-evaporite mineral formation that is the mining intervalto prevent contact of mining solutions with natural rock and aquifersoutside the area of the formation intended for mining. Generally, theaccess well primary casing is installed, cemented, and bonded to thewall of the borehole preferably from the end of the casing and up to thesurface. The term casing refers to a pipe that is installed in theaccess well. A casing shoe is attached to the lower extremity of thecasing to assist running the casing into the hole and cementing tocreate a casing to rock seal.

The at least one access well may be a single access well or two or moreaccess wells. There is no upper limit on the number of access wells;instead, one skilled in the art can develop mining plans andconfigurations appropriate to the site and resource being mined inaccordance with the methods of the present invention and determine theproper number of access wells accordingly.

The method further includes drilling at least two lateral boreholes,wherein the lateral boreholes communicate with each other and wherein atleast one of the lateral boreholes is connected to at least one accesswell. Although the modifier ‘lateral’ is used to describe this type ofborehole, it is to be understood that the term lateral generallyindicates a borehole that is not an access well, and does notnecessarily indicate the directional axis of the borehole's run. Lateralboreholes may extend in any direction relative to the access well,including substantially parallel to or continuing out from the accesswell. A lateral borehole typically has at least a portion of theborehole that is mineable or leachable, e.g., where the natural rock ormineral formation surrounding the borehole is exposed, and wherein asolution mining fluid can contact the natural rock or mineral formation.Lateral boreholes may have a number of configurations along theirlength, including a number of different types of curvatures. Typically,a lateral borehole will extend through an evaporite mineral or permeableore mineral formation. A typical lateral borehole will extend from wherethe drill branched out from another borehole (lateral or access) untileither the end of the drilling or until another branching occurs. Alateral borehole may also refer to a non-cased and non-cemented boreholethat has a direct (i.e., non-branching) connection to an access well.Lateral boreholes are often referred to more simply as laterals.

Any number of lateral boreholes may be drilled in accordance with amining plan developed in accordance with the methods of the presentinvention. There may be at least three lateral boreholes, at least fourlateral boreholes, at least five lateral boreholes, or at least sixlateral boreholes or more. Underground configurations of the presentinvention typically have a high ratio of lateral boreholes to accesswells. For example, there may be a ratio of lateral boreholes to accesswells of equal to or greater than about 1:1 (i.e., number of lateralboreholes:number of access wells); greater than or equal to about 2:1;greater than or equal to about 3:1; greater than or equal to about 4:1;or more.

The lateral boreholes are drilled such that they are in communicationwith each other. Communication refers to an open connection betweenboreholes such that, for example, a solution mining fluid can flow fromone borehole into another. At least one of the at least two lateralboreholes is connected to (i.e., is in borehole communication with) atleast one access well. Accordingly, each lateral borehole is connectedto another borehole in at least two separate points. A lateral boreholemay connect to an access well and another lateral borehole, or it mayconnect at two points or more to at least one other borehole or to morethan one borehole. The lateral boreholes are connected to one another,or interconnected, at one single, multiply connected point.

To drill boreholes in accordance with the present invention,oil/gas/water drilling tools, techniques and services may be used. Thesetypes of tools may require adaptation as the evaporite ores can beincompatible with some of the more common drilling fluids and softevaporite ores can create steering problems.

Directional drilling may be accomplished by the application of pressureagainst the side of the borehole to direct the bit in the oppositedirection. The steering pressure point or points can be 40′ behind bit,allowing drilling fluid the time to leach, weaken, or erode thewellbore. If the hole is washed out (mechanical erosion) or dissolved atthe point of required contact or weakened sufficiently that it cannotsupport the required pressure, then directional drilling may beimpractical. Successful directional drilling requires protecting theborehole from leaching, weakening and erosion. In the case ofwater-soluble ores, oil based drilling mud work can be used to protectthe borehole. A less messy and lower cost alternative that is oftenfound to provide sufficient wellbore protection is altering thechemistry of the water based drilling mud system. As an example, saltsaturated drilling mud has been found useful in directionally drillingnahcolite, as nahcolite is nearly insoluble in salt saturated solutions.Alternatively, as nahcolite is naturally occurring baking soda,pre-saturating the direction drilling mud with baking soda has beenfound to protect the wellbore.

Borehole protection is also needed to prevent keyholing, a drilling termfor a smaller diameter drill pipe slot cut into the inside of a curve. Akeyhole can trap the drilling assembly when drilling out of the hole ifa larger diameter drilling assembly is pulled into the smaller diameterkeyhole slot. To avoid becoming stuck in the hole, drill bit cuttingsmust be cleared from the borehole quickly and efficiently. Horizontalboreholes are hard to clean, as the cuttings tend to lie down and allowthe mud to slip past. The assistance provided by rotating the drill pipeand the drilling assembly is not always available when steering manytypes of directional drilling tools. Drilling in such conditionsrequires good mud and careful drilling. Careful drilling allows theoperator to feel the increasing drag as cuttings build up in time toreact using special measures to clean the hole before getting stuck.Techniques to clean the hole include such techniques as sliding thedrill assembly in and out of the hole until the drag of the cuttings iscleared. If this occurs too often, improved mud chemistry, viscosity,and velocity may be required. The ability to increase mud velocity, whendirectionally drilling, may be limited, as doing so can disrupt the bitrotational speed and performance. Failures of mud chemistry andviscosity have been linked to adverse reactions with the solution miningores. Mud experts are preferably contacted before drilling to properlydesign the mud system to clear the cuttings and protect the borehole'sability to support the directional drilling pad pressure. During actualdrilling, the same expert should preferably provide continuous mudmonitoring, evaluation and instructions to the driller.

In drilling evaporite mineral beds, once the drilling system is tuned inthe field to protect the wellbore and provide the push needed to steerthe drilling assembly, drilling is typically fast and easy compared tooil/gas/water drilling. Accordingly, extensive lateral borehole systemsinvolving long lateral and numerous branching can be achieved atreasonable cost. Boreholes of about a mile in length may be achieved.Drilling lateral boreholes off of another borehole or directly from anaccess borehole is a procedure established in the oil/gas drillingindustry. However, the ease of drilling in evaporite minerals makes thecreation of lateral boreholes in such formations economically feasible,especially considering the advantages in increased solution miningefficiency.

Drilling of lateral boreholes in hard rock is often accomplished using awedge set in the first borehole to deflect the drilling assembly intofresh rock. In most evaporite solution mining applications, thefollowing more efficient method may be used instead. The method firstincludes drilling a first lateral borehole in a first direction having aforward end on a first plane. More specifically, after a first curve isdrilled, the tool is returned to the beginning of the first curve andpointed to drill a curve in the opposite direction. The method can alsoinclude the step of reciprocating the drill from the forward end of thefirst lateral borehole to expand the first lateral borehole to include asecond plane. More specifically, the bit is positioned so that it iscutting the backside of the initial curve, and the drill is reciprocateduntil a ledge is built on the backside of the initial curve, creatingthe second plane. When the bit can stand on the ledge and take weight,directional drilling of the second lateral borehole in the second planecan proceed as planned. While it is often impractical to reenter thefirst curve and lateral borehole once the second lateral borehole hasbeen drilled off the backside, it is possible to drill off the backsideof the second lateral borehole curve. Therefore, a third curve andlateral borehole can be extended off the second curve and lateralborehole, and the fourth curve and lateral borehole can be extended offthe third, and so on. Creation of additional lateral boreholes maycontinue as long as keyholing and friction are under control. Connectionof all of the lateral boreholes at or close to their furthest ends maybe done by drilling yet another lateral borehole which intersects theseends. Drilling assembly and tubing reentry to the first drilled curveand lateral is possible using the emerging oil drilling tools andtechniques.

The accuracy and precision required to drill interconnected lateralborehole systems can be achieved by standard directional drillingassemblies when combined with knowledge and observation of the geology,lithology, cuttings, drilling rate, geophysical logging and othergeologic and drilling indicators. For example, in stratified formationsa pair of boreholes could be intersected with confidence by drillingeach along a geologic contact at a sufficient intersecting angle.

Curvature of the lateral boreholes is determined by the angle build rateof the drilling assembly and completion requirements. The angle buildrate is commonly expressed in degrees of angle gained per 100 feet ofdrilling. Currently, the allowable bending limitation of the largerdiameter casing and tubing often used in solution mining applications issuch that the preferred angle build rate is about 8 to 12 degrees per100 feet. An 8-degree build rate is about a 700-foot radius curve and a12-degree build rate about a 500-foot radius curve. Angle build rates ofabout 12 degrees to about 20 degrees may also be used with specialapplication casing or smaller diameter casing. It is important to fullyexamine the tightest portion of the curve and the limitations of thetubing joints that are bent and then operated in corrosive conditions,and subject to heating/cooling induced stress cycling.

Preferably, the boreholes are positioned such that at least a portion ofthe lateral boreholes are between about 25 feet and about 750 feet indistance from each other. Also preferred are distances of between about50 feet and about 500 feet from each other; distances between about 100feet and about 400 feet from each other, and distances from about 200feet to about 300 feet in distance from each other. A more preferreddistance from each other is between about 250 feet and about 275 feet indistance from each other.

The lateral boreholes may be disposed in any position relative to eachother. In a preferred embodiment, at least a portion of the lateralboreholes is disposed substantially vertically with respect to eachother. In another preferred embodiment, at least a portion of thelateral boreholes is disposed substantially horizontally with respect toeach other. One of skill in the art with the knowledge of the presentinvention will be able to determine how to position the lateralboreholes with respect to each other for efficient mining of theresource. As an example, multiple horizontal evaporite beds can besimultaneously solution mined using a vertically stacked set ofhorizontal laterals where a lateral is placed in several of thehorizontal beds and joined and mined with circulation in series.

Cavities developed by solution mining can quickly become so large thatthe injection and recovery flows cannot directly influence the flow in acavity in a significant way. However, strong flow and mixing within acavity is generally desirable to accomplish improved mining efficiencyand resource recovery. Specific gravity gradients can be utilized todrive high flow rates and mixing within a cavity. The specific gravitygradients are created as the solvent absorbs the dissolved minerals and,in some cases, by solution temperature changes. Temperature changes canoccur as heat is transferred to or from the earth and by endothermic andexothermic dissolution and precipitation chemistry. Large mass flow andmixing occurs when lighter specific gravity solvent enters the cavity atthe bottom and rises to the top, drawing and mixing large volumes ofsolvent in the cavity. Factors that can be used by one expert in thefield to utilize this cavity flow and mixing concept include chemistry,specific gravity gradient, viscosity, bed thickness, cavity size, cavityshape, and the amount and nature of the insoluble matter. As example,very high temperature can excessively break down the insoluble debrisresulting from the dissolution process filling the cavity with a mushthat chokes the desired flow and mixing within the cavity.

In order to more efficiently mine the bedded resource, the methods ofthe present invention may further comprise placing an artificial leachbarrier within at least one lateral borehole to control the leach rateand direction of leaching of the minerals within the cavity or porousformation. Preferably, the artificial leach barrier is a gas and/orpetroleum fluid and the cavity must be able to contain such liquid. Suchartificial leach barriers are commonly used to improve the performanceof vertical well solution mining methods. They work by controlling therelative vertical and horizontal leach rates to gain a preferred cavityshape. One skilled in the art can readily apply and benefit by the useof artificial leach barriers with the present invention.

In another embodiment of the present invention, methods of the presentinvention may further comprise drilling at least one of the lateralboreholes such that a natural barrier controls the relative vertical andhorizontal leach rates to gain a preferred cavity shape. A horizontalnatural barrier may preferably lie between the two lateral boreholes.The natural barrier may be either an intrabed natural barrier or aninterbed natural barrier. Natural leach barriers are particularly usefulfor horizontal beds where applying an artificial leach barrier may bemore difficult. An example of a natural intrabed barrier is a thininsoluble stringers lying within a bed. An example of a natural interbedbarrier is an intervening layer of non-evaporite minerals between beds,such as a shale interval. One skilled in the art can identify and use ofnatural leaching barriers to improve the performance of the presentinvention. Natural leach barriers may be identified by study of geologicrecords such as exploration cores and well logs. Barriers may also bediscovered during pilot or commercial mining operations by carefulmonitoring and observation.

As example, intrabed natural barriers can be used to favorably influencesolution mining performance. Even in rich evaporite mineral beds,generally there is a significant insoluble content and the geologicdeposition often may have consolidated the insoluble material intonumerous stringers interspersed in the bed. A single insoluble stringeror, preferably, a series of insoluble stringers act as leach barriersand can be used to improve the solution mining performance in a mannersimilar to use of the massive natural barriers described above.

To mine matrix ore bodies, for example a nodular and crystallinenahcolite contained in a nearly impervious oil shale formation, thesolvent and mining plan will preferably cause the failure of the nearlyimpermeable matrix containing the desired mineral. The failure can beinduced chemically and/or mechanically. Previous patents teach how theoil shell matrix containing nahcolite may be heated to sufficiently to‘retort’ the organic content of oil shale producing a crude oil-likesubstance. In a preferred embodiment, a lower temperature increase canavoid producing a crude oil but cause the oil shale to mechanically failand expose the nahcolite to the solvent. A preferred lower solutionmining temperature is about 100° F. above in situ temperature.Accordingly, a fluid may be injected into the lateral boreholes at anelevated temperature sufficient to attain a cavity that is about 100° F.above the in-situ rock temperature.

To mine a massive resource, traditional vertical independent wells minecylinder shaped cavities hundreds of feet in diameter and height. Often,a long period of unproductive undercut mining is required to accomplishthe preferred cavity size and shape. Methods of the present inventionmay be used to mine massive resources to reduce this unproductiveperiod.

Once mine boreholes are drilled, methods of the present inventionfurther include injecting a fluid into at least one access well. In oneembodiment, the fluid may be injected from the shoe of the access wellvia injection into a lateral borehole. In various embodiments, the stepof injecting a solvent into the at least one access well comprisesinjecting solvent through at least one tubing inserted into the accesswell or alternatively through an annulus defined by tubing in an accesswell. The fluid may exit the access well at the shoe of the access well.Alternatively, the tubing may be used to inject fluid into the lateralboreholes at locations other than the shoe of the access well, forexample by insertion of the tubing some distance into the lateralborehole and directly injecting at the end of the tubing that is at somedistance from the shoe of the access well. Placement of the injectiontubing and injection point(s) preferably stimulates convective flowwithin the lateral boreholes. Tubing may be moved within the boreholesto change the actual fluid injection point. Additionally, tubing may beplugged to close off an injection point and perforated or parted tocreate a new injection point.

If multiple injection points are desired, injection can be made throughan access well, from more than one access well, or through multipletelescoping tubings. In a preferred embodiment, the step of injecting afluid comprises injecting fluid from more than one tubing inserted intothe access well. For example, an access well connected to a lateralborehole can have a first tubing running from the surface through theaccess well and into the lateral borehole a first distance. Thisassembly can include a second tubing, smaller in diameter than thefirst, running through the first tubing and extending out the end of thefirst tubing into the lateral borehole a second distance. This assemblyallows for injection of fluid at three points. The first injection pointis at the connection of the access well and the lateral borehole throughthe annulus defined by the access well and the first tubing. The secondinjection point is at the point where the second tubing exits the firsttubing through the annulus defined by the first and second tubings. Thethird injection point is at the end of the second tubing. Open-holeplugs may be used to seal off the borehole to direct the flow path offluids in the mine or well.

Enhanced mining efficiency can often be gained by periodic flow reversalof the injection points and the collection points (as described below)and changing the injection and recovery point locations in the boreholeand cavity system. Flow reversal is accomplished by changing the pipingarrangement on the surface. Relocation of the injection and recoverypoints is accomplished underground. In some cases, the tubing extendedinto the lateral can be slid in or out to adjust the injection andrecovery points. Injection and recovery points can be adjusted withoutmoving the tubing by plugging and perforating or parting using knowntechniques. Lateral holes can be extended or new lateral holes from theaccess well or from previously drilling lateral borehole can be drilled.Solution mining systems and mine plans include the use of boreholes,casings, cement, tubing, tubing packers, plugs, packers andperforations, and, subsequent expansion and modification of the these isaccomplished by adapting tools, techniques and services developed in theoil and gas drilling and production industry.

A solution mining fluid is any type of fluid that has the capacity todissolve an evaporite or non-evaporite mineral. Preferably, the fluid isa solvent. An appropriate solvent can be determined by those of skill inthe art depending on what mineral is being mined. The solvent is at atemperature suitable for dissolution of the evaporite mineral. In someembodiments, the solvent is heated and it can be heated to a temperaturegreater than about 10° C. or about 50° C. and can be heated up to about95° C. or about 110° C. In a particularly preferred embodiment, thesolvent is at significantly higher temperatures, as described below.

In one embodiment, the solvent avoids problems associated with what hasbeen incorrectly identified as incongruent leaching of minerals. Fortrona solution mining, the basic solubility knowledge required to designa trona solution mine and produce trona and/or related compounds islargely available in Garrett, Natural Soda Ash. [Van Nostrand Reinhold]See also Example 1. The phase diagram describing the solubility andsolid phases of the Na₂CO₃—NaHCO₃—H₂O system is well known in the art.Those skilled in the art will recognize that if trona leaching isinitiated with pure water as the solvent, the ions associated withsodium bicarbonate become saturated, before those associated with sodiumcarbonate, and may precipitate in the cavity. This can be avoided, ifdesired, by injecting the barren solvent resulting from cooling orcooling and evaporative crystallization of sodium sesquicarbonate orsodium bicarbonate. In either case, the trona depleted solvent can beheated and used as the injection solvent to dissolve trona without theso called incongruent leaching problems. Preferably, the solvent isheated and injected at about 130° C. and recovered at about 120° C. andcooled to about 30° C. producing sodium sesquicarbonate. In this case, aso called congruent leaching solvent results from heating the 30° C.solvent to the 130° C. injection temperature. Another example withoutlimitation is when the solvent is heated to about 105° C., recovered atabout 95° C., carbonated and cooled to about 30° C. to produce sodiumbicarbonate. It is well known that a so called congruent leachingsolvent can also be prepared by adding sufficient soda ash and/orcaustic soda and/or lime to water. To those skilled in the art, it isapparent that direct crystallization of a range of trona relatedcompounds such as sodium bicarbonate, monohydrate soda ash, decahydratesoda ash and anhydrous soda ash is possible at various temperaturesafter adjusting the carbonate and bicarbonate ion balance using knownprocesses. Congruent solvents for solution mining can also includecarbonic acid, sodium hydroxide and/or calcium hydroxide, in addition tosodium carbonate.

To avoid leaching salt that can naturally accompany trona in the ground,the trona can be solution mined with aqueous solutions presaturated withsalt. As an example, sufficient hydroxide is added to the injectedsolvent to chemically convert the bicarbonate ions to carbonate ions atthe point of dissolution resulting in salt brine rich in soda ashrelated ions that yields soda ash on cooling and/or evaporativeconcentration. Alternatively, several known processes can be used tosimultaneously produce marketable trona, other trona related productsand rock salt. The use of lime and hydroxide to improve salty tronasolution mining is an example without limitation of the use of lime andhydroxide in the solution mining of trona and processing sodiumcompounds.

The widely used (low cost) source of hydroxide in the trona mining andsodium processing industry is lime (Ca(OH)₂). It is widely used toconvert bicarbonate ions to carbonate ions as part of various well knownprocesses. A well-known problem with use of lime in surface processes isthe resultant limestone (CaCO₃) precipitation. Removal and disposal ofthe precipitated limestone is costly. The limestone removal and disposalneed not be a problem for solution mining as the precipitated limestonecan remain in the cavity as precipitated or be slurried into the cavityfor disposal if precipitated in a surface process.

One embodiment of the present invention includes injection of an aqueoussolution, such as, substantially pure water, including, for example,very pure condensed steam or sodium decahydrate depleted solutionscontaining up to 6% Na₂CO₃ and 5% NaHCO₃, at a temperature sufficient tomaintain the borehole and cavity dissolution system in theWegscheiderite solid phase region shown on the phase diagram FIG. 14.For example, the temperature of the injected solution and/or therecovered (or removed) solution can be at least about 90° C., 95° C.,100° C., 105° C., 110° C., 115° C., 120° C., 125° C., 130° C., 135° C.,140° C., 145° C., 150° C., 155° C., 160° C., 165° C., 170° C., 175° C.,180° C., 185° C., 190° C., 195° C., 200° C., 205° C., 210° C., 215° C.,220° C., 225° C., 230° C., 235° C., or 240° C. Such a cavity at restbecomes double saturated at temperatures and concentrations shown at thecontact line of trona and Wegscheiderite solid phase regions. At 90° C.,this is 18.2% Na₂CO₃ and 10.1% NaHCO₃. At 100° C., this is 21.5% Na₂CO₃and 9.3% NaHCO₃. At 110° C., this is 24.1% Na₂CO₃ and 9% NaHCO₃.Preferably the cavity is operated such that the recovery temperature andconcentrations approach the TWA triple point where the maximumconcentration of 25.8% Na₂CO₃ and 9% NaHCO₃ is achieved at 117° C.Temperatures above the TWA point reduce the concentration of thesaturated solutions. At 120° C., the concentration reduces to 25.6%Na₂CO₃ and 9% NaHCO₃. At 130° C., the concentration reduces to 24.8%Na₂CO₃ and 9% NaHCO₃. At 140° C., this is 24.3% Na₂CO₃ and 9% NaHCO₃.Temperatures below the TWA point also reduce the concentration of thesaturation solutions. At 115° C., the concentration reduces to 25.1%Na2CO3 and 9% NaHCO3. At 110° C., the concentration is reduced to 24%NaCO3 and 9% NaHCO3. Consequently, in further preferred embodiments, thetemperature of the injected solution and/or the recovered (or removed)solution can be in the range of between about 90° C. and about 240° C.,between about 100° C. and about 190° C., between about 105° C. and about170° C., between about 110° C. and about 145° C., between about 115° C.and about 120° C.

Another aspect of the invention is that by solution mining in accordancewith the teachings herein, solution mining of trona deposits can beconducted at about the TWA point for a given deposit such that themining solution as it is removed is at about the TWA point temperature.At precisely the TWA point temperature, the mining solution would be atmaximum solubility of sodium bicarbonate and sodium carbonate achievablein the Wegscheiderite solid phase region. However, it should berecognized that control of temperatures and concentrations in miningsolutions is not absolutely precise. Thus, in other embodiments, thesolution mining of trona deposits is conducted to produce a miningsolution in which both sodium bicarbonate and sodium carbonate are atgreater than about 75% of maximum solubility, greater than about 80% ofmaximum solubility, greater than about 85% of maximum solubility,greater than about 90% of maximum solubility, greater than about 95% ofmaximum solubility, or greater than about 99% of maximum solubility.Further embodiments of the invention include mining solutions per sehaving sodium bicarbonate and sodium carbonate concentrations in theseranges as well.

In one embodiment of the process, the aqueous injection solutioncomprises condensed steam produced by evaporation of water from asolution to produce sodium carbonate products, such as sodium carbonatemonohydrate, for example, from operation of the monohydrate process. Asused herein, reference to the “monohydrate process” refers to a processin which a sodium carbonate solution is treated to produce soda ash byevaporating water from the sodium carbonate rich solution in anevaporator circuit, crystallizing sodium carbonate monohydrate from thepregnant mother liquor. In various embodiments, the condensed steamproduced by evaporation of water from a solution to produce sodiumcarbonate products constitutes at least about 25 wt. %, at least about50 wt. %, at least about 75 wt. %, at least about 90 wt. %, at leastabout 95 wt. %, or at least about 99 wt. % of the aqueous injectionsolution. In various other embodiments, the aqueous injection solutiondoes not include any recycled or recirculated mining solution taken fromthe mining cavity.

This process further includes removing aqueous solution from the cavity,wherein trona from the cavity is dissolved into the solution before itis removed. Alkaline values are then recovered from the removed aqueoussolution by a variety of processes.

During highly saturated operating periods (for example, at low miningrates or when restarting a hot cavity), solution mining with recovery atthe TWA maximum concentration can include dilution of the miningsolution to prevent precipitation blockage of the casing and pipelinesystem because either heating or cooling causes supersaturation. Analternative to dilution is operation where the recovery solutiontemperature is a little below the TWA point so that solution can beheated to a little above the TWA temperature and allowed to coolsomewhat during pipeline transport. A preferred alternative is operationat a temperature a little above the TWA temperature such that thecooling experienced during the pipeline transportation from the cavityto surface and to the processing plant does not supersaturate or causeprecipitation that could obstruct the flow.

The high concentration of the solutions at the TWA point and the reversesolubility at temperatures above the TWA that can be used to avoidpipeline plugging combine to provide a highly productive and easy tooperate trona solution mining opportunity that is easily utilized bythose skilled in the art. Existing facilities can be retrofitted or newfacilities constructed to gain the advantages of this opportunity. Thisprocess is a low cost production opportunity for numerous sodiumproducts such as sodium sesquicarbonate, sodium bicarbonate, sodiumcarbonate monohydrate and anhydrous sodium carbonate using existingprocesses such as fortification, steam stripping, carbonation andnumerous other well-known sesquicarbonate, bicarbonate and soda ashprocesses.

In a further embodiment of the present process, the mining process isconducted until the trona deposits are effectively depleted, asdescribed above. In accordance with the present invention, during thetrona mining, Wegscheiderite and/or nahcolite is precipitated from themining solution. This embodiment of the invention includes furtherinjecting an aqueous solution in a cavity that is effectively depletedof trona and that includes precipitated Wegscheiderite and/or nahcoliteto dissolve the Wegscheiderite and/or nahcolite. The resulting solutionwill eventually become saturated in both sodium bicarbonate and sodiumcarbonate. As the solution is removed from the mine, alkaline values arerecovered from the aqueous solution by conventional processes. In thisembodiment, the temperature of the solution for dissolvingWegscheiderite and/or nahcolite is high enough so that, in preferredembodiments, the removed mining solution is greater than about 30° C.,between about 30° C. and about 240° C., between about 65° C. and about180° C., and between about 100° C. and about 120° C.

A further embodiment of this process includes introduction of lime(Ca(OH)₂) into the underground cavity. In this embodiment, the lime canbe introduced into the cavity at the point at which the mining solutionis being injected. Alternatively, lime can be introduced into the cavityat a point removed from the point at which the mining solution is beinginjected. In either embodiment, the introduction of lime into thesolution having sodium bicarbonate ions will cause the formation ofcalcium carbonate (CaCO₃). Calcium carbonate that is formed will settlefrom the solution and largely be removed from the mining solution priorto removal of the solution from the cavity. In an alternativeembodiment, the process includes removing aqueous solution from thecavity and subsequently introducing lime to the removed solution on thesurface. the introduction of lime into the solution will cause theformation of calcium carbonate (CaCO₃). Calcium carbonate that is formedwill settle from the solution and can be disposed of by introductioninto a mining cavity in a slurry. The mining cavity can be one that isbeing actively mined because the slurried calcium carbonate will settleout of the mining solution and remain in the cavity. Alternatively, theslurried calcium carbonate can be introduced to a mine cavity that is nolonger be actively mined.

With reference to FIG. 15, various preferred embodiments of the presentinvention are illustrated. An aqueous mining solution is introduced toan underground cavity 100 at 120. The underground cavity 100 is a tronadeposit cavity and the mining solution is at a temperature sufficient tomaintain at least a portion of the mining solution in the cavity 100 inthe Wegscheiderite solid phase region and preferably such that therecovery solution is at about the TWA point temperature. As trona in thecavity 100 is dissolved, sodium, carbonate and bicarbonate ions go intosolution in the aqueous mining solution. Mining solution resulting fromthe trona dissolution process is removed from the cavity at 140. Theunderground mining operation can include dilution of the mining solutionand/or addition of heat to the mining solution by introduction ofadditional fluid from a source 160 to the underground cavity 100. Thisstep of dissolution can be used to prevent precipitation blockage of thecasing and pipeline system that may occur due to supersaturation.

An alternate means of preventing precipitation blockage of the pipelineis bring the mining solution removed from point 140 into thermalcommunication with hotter mining injection solution prior to entry tothe cavity at point 120 in a heat exchanger 180. Flow switching,alternating the wells used for injection and recovery, causes theinjection solution to dissolve the precipitation blockage from the wellpreviously in service recovering the solutions. The mining solutionwithdrawn from the cavity of point 140 can be further treated by adegasification and/or filtration process 200. The resulting miningsolution can then be treated by the monohydrate process 220, thesesquicarbonate process 240, or by carbonation to form bicarbonate 260.

Prior to being treated in the monohydrate process 220, the miningsolution can be pretreated by using a number of known processes,including fortification, steam stripping, evaporation, the hydroxideprocess, or the sodium carbonate decahydrate process 280. Carbon dioxideproduced by any of these processes can be recycled 300 for carbonationin the bicarbonate process 260.

After any pre-treatment steps, the mining solution is introduced toconventional monohydrate processing 320. The primary product from themonohydrate process is dense soda ash 340. Water that is driven off fromthe solution as part of crystallization in the monohydrate process canbe condensed, for example, by mechanical vapor recompression. Thetemperature of such a condensate is typically about 125° C. Waste heatfrom the monohydrate process 380 can be introduced to further heat thecondensate. Alternatively, or in addition, start-up or trim heat 400 canbe introduced to the condensate to heat the condensate prior tointroduction into the underground cavity 100.

Prior to treatment by the monohydrate process, the mining solutionexiting the degasification/filtration unit 200 can be treated by thesesquicarbonate process 240. This process involves crystallization ofsesquicarbonate crystals in the solution by cooling and/or evaporation420. The crystals can be dewatered and dried 440 with the liquid 460from the dewatering step being introduced to the monohydrate plant 320.Prior to introduction of the liquid 460 from the dewatering step 440into the monohydrate plant 320, the liquid 460 can be optionally treatedby one of fortification, steam stripping, evaporation, the hydroxideprocess, or the sodium carbonate decahydrate process 280.

The sesquicarbonate crystals 480 that are dewatered and dried are acommercial product or they can be subjected to calcination 500 to form amedium ash product 510 or the medium ash product 510 can be subjected todensification 520 to form a dense ash 530. Alternatively, the wet cakefrom the dewatering step 440 can be introduced to a dissolver 540 withthe resulting solution being introduced to the crystallization step ofthe bicarbonate process 260.

In a further embodiment of the process, the mining solution, prior tobeing subjected to the monohydrate process 220 can be processed bycarbonation of the solution to form bicarbonate 260. Solution exitingthe degasification/filtration operation 200 can be carbonated and thensubjected to crystallization of sodium bicarbonate by evaporation and/orcooling 550. Carbon dioxide for the step of carbonation can beintroduced from the recycle stream 300, the calcination steps 505, 625,or can be introduced as start-up carbon dioxide 560. Excess carbondioxide in this process can be vented 570. In addition, excess CO₂ canbe vented 580 from the carbonation and crystallization operation 550.Sodium bicarbonate crystals produced in the crystallization unit 550 canbe dewatered and dried 590. The resulting liquid 600 can be treated inthe same manner as the liquid 460 from the dewatering process 440.Namely, the liquid can be optionally treated 280 or introduced directlyinto the monohydrate plant 320. Liquid 600 can alternatively be fed tothe process 420. In a further alternative embodiment, the liquid 600 canbe fortified 605 with additional sodium carbonate values, such as fromtrona ore or off-spec sodium products. The crystals resulting from thecrystallization process 550 can be used directly as a sodium bicarbonateproduct 610. Alternatively, the sodium bicarbonate can be calcined 620to form light ash 630. The light ash can be further densified 640 toform dense ash 650.

Once fluid is injected in the boreholes, the method further includescirculating the fluid through at least one access well and at least twolateral boreholes wherein controlled fluid flow is maintained between atleast two lateral boreholes. Circulation of fluid can be achieved in anumber of ways. Circulation may be achieved by the inlet fluid pressurecaused and maintained by injection of the fluid into the mine.Circulation may also be achieved by mine design and fluid injectionpoints that utilize the presence of natural convective flow caused bydiffering densities of barren and pregnant solutions. Gas lift andelectrical-mechanical pumps can also be used to circulate the miningfluids.

When more than one lateral borehole is being solution mined at the sametime, substantially equal or controlled fluid flow is maintained betweenthe lateral boreholes. Controlled flow, in the context of thisinvention, refers to fluid flows that are similar enough that one of thetwo or more lateral boreholes is not effectively blocked or pluggedand/or that rates of mining and/or borehole enlargement are similarbetween at least two lateral boreholes. To determine whether a boreholeis flowing, plugs may be inserted to test each individual lateralborehole for flow. Boreholes, particularly after a period of solutionmining, may vary in size, causing the flow rate to differ between theboreholes. However, there should be measurable flow in each lateralborehole. Preferably, the values for the flow rates (e.g., in terms ofvolume per time) between at least two of the lateral boreholes arewithin about 50%, more preferably about 30% and more preferably about15% of each other.

In one embodiment, the circulating step includes flowing the fluidthrough the at least two lateral boreholes in a parallel flow. Aparallel flow indicates that all the lateral boreholes contain fluidtraveling in the same direction through the boreholes. In this flowconfiguration, generally plugs are not placed within the lateralboreholes to influence flow direction. Another characteristic ofparallel flow is that fluid in one lateral borehole will not thuscirculate the full length of another lateral borehole, but rather, willtypically connect with an access well or with an access well aftertraversing less than the full length of another borehole.

In another embodiment, the circulating step includes flowing the fluidthrough the at least two lateral boreholes in a serial flowconfiguration. Plugs, tubing packers, and tubing may all be used toforcefully circulate fluid in a serial flow through the lateralboreholes. Such a serial flow has the benefit of forcing solution miningof each borehole. If one borehole becomes restricted of stops flowing,the entire flow circuit is interrupted and the miner has early notice ofthe problem. In one embodiment, serial flow is achieved by the placementof at least one plug in the at least two boreholes which communicatewith each other.

Methods of the present invention further include collecting a pregnantsolution containing a dissolved evaporite mineral. Collection may bedone in a similar manner and with similar equipment as described forinjection. In one embodiment, the step of collecting the pregnantsolution containing a dissolved evaporite mineral comprises collectingsaid pregnant solution at the shoe of the well at the access well. Inanother embodiment, the fluid is collected in the annulus of the accesswell. In another embodiment, the step of collecting a pregnant solutioncontaining a dissolved evaporite mineral comprises collecting saidpregnant solution with at least one tubing placed within an access wellinto at least one lateral borehole. Placement of the collection tubingand collection point(s) is preferably designed to take advantage ofnatural convective flow within the lateral boreholes. Tubing may bemoved within the boreholes to change the actual fluid collection pointafter a period of collection at one point. Additionally, tubing may beplugged to close off an collection point and the tubing can be cut orperforated to establish another collection point.

A number of injection and collection plans are contemplated by thepresent invention. One preferred method for solution mining isimplemented by injecting fluid in the at least one tubing or frommultiple tubings or multiple injection points and extracting thesaturated fluid through the annulus between the tubing and the accesswell cemented casing (i.e., the ‘shoe’ of the well.) Another preferredmethod for solution mining includes the step of injecting through theannulus and producing via the tubing or multiple tubings. In anotherembodiment, the at least one access well comprises a first and secondaccess well, and the step of injecting a solvent comprises injecting thesolvent through the annulus or through at least one tubing inserted intothe first access well, and the step of collecting a pregnant solutioncomprises collecting the pregnant solution from the annulus or from atleast one tubing inserted into the second access well.

In another embodiment of the present invention, there is provided amethod for solution mining of an evaporite mineral that includesdrilling at least one access well accessing an evaporite mineralformation and drilling at least two lateral boreholes. The at least twolateral boreholes communicate with each other and at least one of thelateral boreholes is connected to an access well. The method furtherincludes injecting a fluid into the at least one access well, andcirculating the fluid through the at least one access well and the atleast two lateral boreholes in a serpentine flow pattern. The methodfurther includes collecting a pregnant solution containing at least onedissolved evaporite mineral.

A serpentine flow refers to a serial flow pattern, e.g. a flow patternthat starts with the fluid being injected at one point or end, andflowing through all of the boreholes sequentially until the exit point.Plugs, tubing packers, and tubing may all be used to forcefullycirculate fluid in a serpentine flow pattern through the lateralboreholes. Such a serpentine flow has the benefit of forcing solutionmining of each borehole. In one embodiment, serpentine flow is achievedby the placement of at least one plug in the at least two boreholeswhich communicate with each other.

FIGS. 1 through 6 provide examples of a solution mining system preparedin accordance with the present invention. FIG. 1 shows a single accesswell system having two lateral boreholes for solution mining. Accesswell A1 (only its it lower extremity of the access well shows in thisand other figures) is drilled and completed to access a mineralformation for solution mining. The view of the figure could be anoverhead or side view relative to the ground surface depending on theresource to be mined and the mine plan. The access well is drilled tointercept the solution mining interval in a preferred manner, cased andcemented to bond the casing to the borehole. For one scenario the accesswell is conventionally drilled from surface vertically for some distanceand then directionally drilled to become tangent with the floor of anearly horizontal bedded evaporite bed. At this point, drilling isstopped, the drill string and drilling assembly (not shown) are pulledout, casing AA is run from surface to near the bottom of the access wellborehole as shown and is cemented to bond the casing to the boreholewall preferably from the lower end of the casing to the ground surface.At this point, the access well is used to drill the lateral boreholespreferably using a smaller diameter directional drilling assembly sothat it can pass inside the access well to drill the lateral boreholes.Lateral borehole A11, with connection to an access well, is drilled inan S configuration away from the extended centerline of access well A1and then curved back to parallel that centerline for some distance topoint AB. The directional drilling assembly is then returned to thebeginning of the initial curve of lateral borehole A11 and a lateralborehole A12 is drilled to branch off the backside of that curve andextend substantially along the extended centerline of access well forsome distance before being its drilling is steered to communicate withlateral borehole A11 at point AB. Accordingly, lateral borehole A11 hasa first end in communication with access well A1 and a second end incommunication with lateral borehole A12 at point AB, and lateralborehole A12 has a first and second end in communication with lateralborehole A11. Tubing AC, with packer, (packers are shown in this andother figures as an individual packer but it understood that one skilledin the art may use more than one packer and that a packer or packers canbe used in combination with cement or other substance that assistsborehole and cavity isolation in accordance with the mine plan) isinstalled from surface and set near the first end of lateral boreholeA12 and tubing AD, without packer, is installed from surface to near thesecond end of lateral borehole A12. Mining would proceed with solventinjection from the ends of tubing AC and AD and recovery from the shoeof the access well A1. At intervals in the solution mining process theinjection and recovery flows are reversed and tubing AD can be advancedor withdrawn or plugged and perforated to improved resource recovery byaltering the injection/recovery locations. Should a mine plan requirethe tubing extended into both laterals A11 and A12, the drillingindustry provides the means to do so. Tubing only in the last drilledlateral is preferred as it is easiest to accomplish and often providessufficient flow distribution.

FIG. 2 provides another example of a solution mining system prepared inaccordance with the present invention. FIG. 2 shows a single access wellsystem having four lateral boreholes for solution mining a mineralresource. Access well B1 is drilled to access the mineral formation. Theview of the figure could be an overhead or side view relative to theground surface depending on the resource to be mined and the mine plan.The access well is drilled to access the resource in a preferred manner,cased and cemented to bond the casing to the wall of the access wellborehole. For one scenario the access well is conventionally verticallydrilled from surface for a distance and then directionally drilled tointercept the solution mining interval such that laterals extended fromaccess well B1 can be tangent with and extend along the floor of anearly horizontal bedded evaporite bed for a great distance. At thispoint, drilling is stopped, the drill string and drilling assembly (notshown) are pulled out, casing BA is run from surface to near the bottomof the access well borehole as shown and is cemented to bond the casingto the borehole wall preferably from the lower end of the casing to theground surface. At this point, the lateral boreholes are drilledpreferably using a smaller diameter directional drilling assembly sothat it can pass inside the access well to drill the lateral boreholes.The first lateral borehole B11 is drilled in an S curve manner,previously described, to point BB. Lateral B12 is drilled second off thebackside of the second lateral B11 curve in an S manner to extend forsome distance substantially parallel with lateral B11 to point BC.Lateral B13 is drilled third off the backside of the second curve oflateral B12 in an S curve manner and extended substantially parallel tolateral B11 to point BD. Lateral B14 is drilled fourth off the backsideof the initial curve in lateral B11 to extend for some distancesubstantially parallel the extended centerline of access well B1 for adistance where it is steered to communication with laterals B11, B12 andB13 at points BB, BC and BD respectively.

Accordingly, lateral borehole B14 has a first end in communication withlateral B11 and a second end at point BD having communication with thesecond ends of laterals B11, B12 and B13 noted as points BB, BC and BD.Tubing BE, with packer, is installed from surface and set in the firstend of lateral B14. Tubing BF, without packer, is installed from surfaceto just short of point BB in lateral B14. Tubing BG, with packer, isinstalled from surface and set just short of point BC in lateral B14.Tubing BH, with packer, is installed from surface and set near end oflateral B14 just short of point BD. Mining can progress with solventinjection from tubing BE, BF, BG and BH, in which case, pregnantsolution is collected at the shoe of access well B1. In this manner,measurable forced flow is achieved in all laterals and each lateral hasa source of fresh injection fluid. At intervals in the solution miningprogram, the injection and recovery flows are reversed to improve miningperformance. Except for laterals B11 and B14 (that are mined in series)the laterals can be mined simultaneously or individually. This providesthe miner operating flexibility. In this example and the other examples,one skilled in the art will find use for more or less laterals, tubing,tubing packers.

FIG. 3 provides another example of a solution mining system prepared inaccordance with the present invention using a parallel flow of fluid forsolution mining. FIG. 3 shows a single access well system having fivelateral boreholes for solution mining a mineral resource. Access well B1is drilled to access the mineral formation to be solution mined. Theview of the figure could be an overhead or side view relative to theground surface depending on the resource to be mined and the mine plan.The access well is drilled, cased and cemented to bond the casing to theborehole of the access well. For one scenario the access well C1 isconventionally vertically drilled to the top of a solution mininginterval. At this point, drilling is stopped, the drill string anddrilling assembly (not shown) are pulled out, casing is run from surfaceto near the bottom of the access well borehole as shown and is cementedto bond the casing to the borehole wall preferably from the lower end ofthe casing to the ground surface. At this point, the lateral boreholesare drilled preferably using a smaller diameter directional drillingassembly so that it can pass inside the access well to drill the lateralboreholes. The first lateral borehole C11 is drilled in an S curvemanner, extended substantially parallel to an extension of the accesswell centerline and then curved back to that centerline to intersect thecenterline extension at point CA. Lateral C12 is drilled second off thebackside of the second curve of lateral C11 in a S manner, extendedsubstantially parallel a extension of the access well and then curvedback to point CB to communicate with the third curve of lateral C11.Lateral C13 is drilled third off the backside of the first curve oflateral C11 in an S curve and extended substantially parallel to otherlaterals and then curved back to communicate with lateral C11 at pointCA. Lateral C14 is drilled fourth off the backside of the second curvein lateral C13 in an S curve and extended substantially parallel to theother laterals and then curving back to communicate with lateral C13 atpoint CC. Lateral C15 is drilled fifth off the backside of either of thefirst curves of lateral C11 or C13 and extended to communicate withlaterals C11 and C13 at point 33.

Accordingly, lateral C15 has a first end in communication with lateralC11 or C13 and a second end in communication with laterals C11 and C13at the single, multiply connected point CA; lateral borehole C11 has afirst end in communication access well C1, communication with the secondend of lateral C12 at point CB and a second end in communication withlaterals C15 and C14 at the single, multiply connected point CA; lateralborehole C12 has a first end in communication with the second curve oflateral C11 and a second end in communication with lateral C11 at pointCB; lateral borehole C13 has a first end in communication with the firstcurve of lateral C11, communication with the second end of lateral C14at point CC and a second end in communication with laterals C11 and C15at point CA; and lateral C14 has a first end in communication with thesecond curve of lateral C13, and a second end in communication with thethird curve of lateral borehole C13 at point CC. Tubing CD, with packer,is installed from surface and set near the first end of lateral C15 asshown. Tubing CE, without packer, is installed from surface to near thesecond end of lateral C15. Mining would progress with solvent injectionfrom the shoe of access well C1 and tubing CD into all the lateralboreholes in a substantially parallel manner. The pregnant solution iscollected with recovery tubing CE. At intervals in the solution miningprocess, the injection and recovery flows can be reversed and tubing CEcan be advanced or retracted or plugged or perforated to move improvedresource recovery. FIG. 3 is two dimension but one skilled in the artwill, for some resources, find application where the preferred lateralsarrangement is a three dimensional rosette. It is not necessary toprovide drilled connection of the lateral second ends if the desiredflow is passing a permeable formation between the laterals such as insolution mining sandstone related uranium ores.

FIG. 4 provides another example of a solution mining system prepared inaccordance with the present invention using a series or serpentine flowof fluid for solution mining. FIG. 4 shows a single access well systemhaving five lateral boreholes for solution mining a mineral resource.Access well D1 is drilled to access the mineral formation to be solutionmined. The view of the figure could be an overhead or side view relativeto the ground surface depending on the resource to be mined and the mineplan. The access well is drilled, cased and cemented to bond the casingto the access well borehole. For one scenario, the access well D1 isdrilled vertically to the top of a multiple, nearly horizontal, beddedevaporite resource (bed 1 top-bed 5 bottom). At this point, drilling isstopped, the drill string and drilling assembly (not shown) are pulledout, casing DA is run from surface to near the bottom of the access wellborehole as shown and is cemented to bond the casing to the boreholepreferably from the lower end of the casing to the ground surface. Atthis point, the lateral boreholes are drilled preferably using a smallerdiameter directional drilling assembly so that it can pass inside theaccess well to drill the lateral boreholes. The first lateral boreholeD11 is drilled to curve about 90 degrees relative to access well D1 tobecome tangent with the floor of bed 1, drilled for a certain lengthalong the floor of bed 1 and then is curved back so that it parallels anextended centerline of access well D1 to point DB. The drill isrefracted and plugs DC and DD are set in lateral D11 to block subsequentcommunication of laterals D12 to D13 and D14 to D15 respectively. Plugs,in this and similar applications used as examples of this invention, maybe a single or multiple mechanical plugs and/or cement or other pluggingsubstances. The direction drilling assembly is then returned to thefirst end of lateral D11 and a second lateral D12 is drilled off theback side of the first curve of lateral D11 for some distance along theextended centerline of access well D1 and then turned about 90 degrees amanner similar to the first curve of lateral D11 to become tangent withthe floor of bed 2 and extend along the floor of bed 2 to intersect andcommunicate with lateral D11 at point DE. The drill is then retracted tothe first end of lateral D12 and lateral D13 drilled in a similar mannerto lateral D12 to become tangent with the floor of bed 3 and extendalong the floor of bed 3 to intersect and communicate with lateral D11at point DF. The drill is then retracted to the first end of lateralborehole D13 and lateral D14 is drilled similar manner to lateral D13along the floor of bed 4 to communicate with lateral D11 at point DG.The drill is then retracted to the first curve of lateral D14 andlateral D15 is drilled in a similar manner to D14 along the floor of bed5 to communicate with lateral D11 at point DB.

Accordingly, lateral D11 has a first end in communication with accesswell D1 and a second end in communication with lateral D15 at point BBand is in communication with laterals D12, 13 and D14 at points DE, DFand DG respectively; lateral borehole D12 has a first end incommunication with the first curve of lateral borehole D11 and a secondend in communication with lateral D11 at point DE; lateral D13 has afirst end in communication with the first curve of lateral 12 and asecond end in communication with lateral D11 at point DF; lateral D14has a first end in communication with the first curve of lateral D13 anda second end in communication with lateral D11 at point DG; and lateralD15 has a first end in communication with the curve of lateral D14 and asecond end in communication with lateral D11 at point DB.

To establish serpentine flow, plugs DC and DD were placed in lateral D11as previously described. Tubing DH, with packer, is installed fromsurface and set in laterals D12 before the lateral D12 and D13 branch.Tubing DI, with packer, is installed from surface and set in lateral 14before the branch of lateral D14 and D15. Tubing D, without packer, isplaced from surface to the near the end of lateral D15 at point DB asshown. Mining would progress with solvent injection from the shoe ofaccess well D1 into lateral D11. Solvent is then conducted through alllateral boreholes in a serpentine or series manner with a flow directionas indicated in FIG. 4, culminating with collection from recovery tubingDJ. At intervals in the solution mining process the injection andrecovery flows are reversed and plugs, tubing packers, and tubing DJ canbe extended or extracted or plugged or perforated to improved resourcerecovery. The ability to independently mining of laterals D11 and D12,D13 and D14 or D15 and the potential to improve resource recovery by sodoing is evident to one skilled in the art. Also evident is the use of asecond lateral D13 curve to communicate the second ends of laterals D13and D14, thus eliminating both plugs DC and DD and the extension oflateral D11 beyond point DE. In either case, all laterals are mined withforced flow and tubing DH and DI can also be used for injection orrecovery.

In FIG. 5, a dual access well system for solution mining a mineralresource is shown. FIG. 5 shows a dual access well system having fourlateral boreholes for solution mining a mineral resource. Access wellsE1 and E2 are drilled to access the mineral formation to be solutionmined. The figure could be an overhead or side view relative to theground surface depending on the resource to be mined and the mine plan.The access wells are drilled, cased and cemented to bond the casing tothe wall of the access well borehole. For one scenario the access wellsare initially drilled down vertically and then directional drilled tointercept the solution mining interval in a preferred manner such astangent with the floor of a nearly horizontal bedded evaporite bed. Atthis point, drilling is stopped, the drill string and drilling assembly(not shown) are pulled out, casings EA and EB are run from surface tonear the bottom of the access well boreholes as shown and are cementedto bond the casings to the borehole walls preferably from the lower endof the casing to the ground surface. At this point, the lateralboreholes are drilled preferably using a smaller diameter directionaldrilling assembly so that it can pass inside the access well to drillthe lateral boreholes. The first lateral E11 is drilled from the accesswell E1 to an angle of 45 degrees and extended a substantial distance topoint EC. The drill is then retracted to the first end of lateral E11and lateral E12 is drilled off the backside of lateral E11, extended inan S curve to become offset and parallel to lateral E11 and extend topoint ED. Similarly, lateral E13 is drilled off the backside of thelateral E12 curve to point EE and lateral E14 is drilled off thebackside of the lateral E13 curve to point EF. Lateral E21 is drilledfrom access well E2 to communicate with the second ends of the lateralsE11, E12, E13 and E14 at points EC, ED, EE and EF respectively.

Accordingly, a first end of lateral E11 communicates with access well E1and a second end in communication with lateral E21 at point EC, thefirst end of lateral E12 communicates with the lateral E11 S curve and asecond end in communication with lateral E21 at point ED, the first endof lateral E13 communicates with the lateral E12 S curve and a secondend communication with lateral E21 at point EE, and the first end oflateral E14 communicates with the lateral E13 S curve and a second endin communication with lateral E21 at point EF. Tubing EG, with packer,is inserted from surface via access well E1 into lateral E12 and setbefore the E12 and E13 branch. Tubing EH, with packer, is inserted fromsurface via tubing EG into lateral E13 and set before the junction oflateral E13 and E14. Tubing EI, with packer, is inserted from surfacevia tubing EH and set in the S curve of lateral E14. Mining can beinitiated by injection of solvent from access well E1, tubing EG, tubingEH and/or tubing EI. Examples of modifications that one skilled in theart may find attractive is using three packers on a single tubing toreplace the telescoped tubing arrangement EG, EH and EI. Another suchexample is using similar tubing/packer arrangements in the lateral E21instead of or to compliment those extending from access well E1. Oneskilled in the art can use such options in a manner to mine the lateralsin series, parallel or individually. One skilled in the art can mine anindividual lateral before drilling and mining the next lateral. Thenumber of possible mining laterals is not limited to the four used inthis example. Possible additional laterals include those that aredrilled from windows cut in the cased and cemented access well E1 toconnect to windows cut in the access well E2.

In FIG. 6, a multi-access well system for solution mining a mineralresource is shown. The FIG. 6 could be an overhead or side view relativeto the ground surface depending on the resource to be mined and the mineplan. The figure demonstrates that one skilled in the art can use anynumber of access wells, lateral wells, tubing strings, packer and plugsin various manners and at various orientations to each other. For onescenario, the access well F1 and its lateral F11 are conventionallydrilled vertically while access wells such as F2, F3, F4 and F5 areradially positioned (not evident in the two dimension figure) around thevertical access well F1 and directionally drilled to serve as conduitsfor laterals drilled along the floor of various beds such thatcommunication to the vertical lateral F11 is achieved in each case. Theaccess wells are cased, cemented, and bonded to the walls of theboreholes as previously described. FIG. 6 depicts this scenario twodimensionally.

Access well F2 has a single lateral F21 extending along the floor of amining bed to communicate with lateral F11. Tubing FA, without packer,is installed from surface into lateral F21 between the access well F2shoe and connection lateral F11. Mining of lateral F21 utilizesinjection and recovery at the shoe of the access well F2, at the tubingFA end and point of communication with lateral F11. Injection andrecovery flows are alternated from time to time and tubing FA isretracted, extended or plugged and perforated to improve miningperformance.

Access well F3 has a single lateral F31 drilled along the floor of amining bed such that it communicates with lateral F11 and continues pastlateral F11 for substantial distance. Tubing FB, without packer, isinstalled from surface in lateral F31 via access well F3 to an initialposition between the access well F3 shoe and lateral F11. Tubing FC isinstalled from surface to near the second end of lateral F31. Mining oflateral F31 involves injection and recovery from points at lateral F11,access well F3 shoe, tubing FB and tubing FC. Injection and recoveryflows are alternated and the tubing FB and FC are extended, retractedand/or plugged and perforated to improve resource recovery.

Access well F4 has three laterals F41, F42 and F43 drilled along thefloor of three mining beds to communicate with lateral F11. Mining is byinjecting or recovering from the shoe of lateral well F4 and thecommunication point with lateral F11. Tubing, packer and plugsarrangements in lateral F11 can force flow mine laterals F41, F42 andF43 independently or in parallel. If mined independently, additionallaterals can be drilled and mined after the initial ones are mined out.The number of laterals that can be mined in this manner is not limitedto three.

One skilled in the art will understand that the FIG. 6 access wells F2,F3 and F4 examples suggest application of numerous multi-lateral peraccess well opportunities included in this invention. For example,access well F5 is conventionally drilled vertically, cased and cementedto the top of the multi-bedded evaporite mineral resource in a mannersimilar to access well F1. Lateral F51 is directionally drilled to curveapproximately 90 degrees to become tangent with and extend along thefloor of the bed 1 (upper most) to communicate with lateral F11 andextend beyond Lateral F11 as previously discussed for lateral F31.Tubing FD and tubing FE, without packers, are installed and used to minein the manner described for tubing FB and FC in lateral F31. In thiscase, there should not be injection and recovery from the shoe of theaccess well F5 and mining in the curve section of lateral F41 should beavoided by positioning tubing FD following the curve during injection orrecovery activity. Likewise, access well F1 should be protected frommining related rock movement by using it and lateral F11 below it forrecovery only and by directing tubing FD and FE injection to avoidexcessive undermining the area below access well F1.

When mining of lateral F51 is complete, tubing FE is pulled andrecovered. Tubing FD is plugged in the second end of the lateral F51curve, severed just above that plug and also pulled and recovered. Thecurve above the plug is cemented up to the near the shoe of access wellF5. Techniques common in the industry are used to cut and recover thetubing and perform the cementing work. Lateral F52 in now drilled fromthe shoe of access well F4 a vertical distance and curved in a mannersimilar to lateral F51 to be tangent with and extend along the floor ofbed 2, to communicate with lateral F11 and extend beyond as previouslydescribed for lateral F31. Lateral F52 is equipped with tubing, mined,and cemented back in a manner like lateral F51 just described. LateralF53 is drilled and used to mine bed 3 and its curved section is cementedwhen mining is completed. This cycle of drilling, mining and cementingback can be repeated for more than the 3 beds used in this example. Theaccess well F5 and its related laterals and mining activity could berepeated in a radial arrangement around the central recovery well F1. Insuch case, as mining advances outward from the center, recovery per footof lateral borehole would increase in geometric proportion to theincreasing area of a circle. One skilled in the art may find resourcesare better mined in this manner beginning with the lower beds andworking successive laterals and mining upward instead of downward as inthis example. In many cases, mining the lower bed first can result ininduced roof failure that progressively solution mines the overhead bedswithout additional drilling.

In another embodiment of the present invention, there is provided amethod for solution mining of an evaporite mineral which includesdrilling first and second access wells extending into an evaporatemineral formation and drilling first and second substantially parallellateral boreholes, wherein each lateral borehole has first and secondends, wherein the second ends of the lateral boreholes communicate andwherein the first end of the first lateral borehole communicates withthe first access well and the first end of the second lateral boreholecommunicates with the second access well. The method further includesinjecting a fluid into the first access well and collecting a pregnantsolution containing a dissolved evaporite mineral from the second accesswell. In a preferred embodiment, the method further includes injecting afluid into the second access well and collecting a pregnant solutioncontaining a dissolved evaporite mineral from the first access well. Inanother preferred embodiment, the first lateral borehole contains atleast one first access tubing and the second lateral borehole containsat least one second access tubing and the method further includesinjecting a fluid into the first access tubing and collecting a pregnantsolution containing a dissolved evaporite mineral from the second accesswell. In yet another preferred embodiment, this method further comprisesinjecting a fluid into the second access tubing and collecting apregnant solution containing a dissolved evaporite mineral from thefirst access tubing. The method also includes the embodiment wherein thelateral boreholes also communicate via first intermediate positions oneach lateral borehole between the first and second ends of each lateralborehole, and the embodiment wherein the lateral boreholes alsocommunicate via second intermediate positions on each lateral boreholebetween the first and second ends of each lateral borehole.

FIGS. 7, 8 and 9 provide an illustration of particular embodimentsdiscussed in the preceding paragraph. While all of the figures containedwithin this disclosure are two dimensional, the three dimensionalapplications will be evident to one skilled in the art. In FIG. 7, adual access well system for mining a bedded evaporite mineral resourceis shown. FIG. 7 could be an overhead or side view relative to theground surface depending on the resource to be mined and the mine plan.The access wells are drilled, cased and cemented from the shoe upward tothe surface. For one scenario the access wells G1 and G2 areconventionally drilled vertically down for some distance. Theconventional drilling assembly is then replaced with a directionaldrilling assembly to advance the access well boreholes in a curve toalmost intercept the evaporite mineral formation near the roof line andparallel to each other and at sufficient angle to allow subsequentlateral drilling to become tangent with the base of the evaporiteformation to be solution mined. Prior to penetrating the roof of theevaporite mineral formation, the drill is stopped, the directionaldrilling assembly (not shown) is pulled out and casing GA and GB areinstalled as shown in the boreholes from slightly above the surface (notshown) to near the end of the boreholes. The casing is then cemented andbonded to the borehole wall, preferably from the end of the boreholes upto the surface. At this point, the lateral boreholes with firstconnection to an access wells are drilled into the bed to be mined andextended within the bed in accordance with the disposition of the beddedresource to be mined (not shown) and the mine plan. Preferably a smallerdiameter directional drilling unit and MWD assembly that can pass withinthe cased access wells is used to drill the first lateral boreholes G11and G12 parallel to each other for a substantial distance and thencurved to create a curvature of approaching 90 degrees to communicate atpoint GC. Accordingly, a first end of lateral G11 communicates withaccess well G1 and a second end of lateral G11 communicates at point 75with lateral borehole G21, and a first end of lateral G21 communicateswith access well G2 and a second end of lateral borehole G21communicates at point 75 with lateral G11. Tubing GD and GE, withoutpackers, are installed from surface via access well G1 into lateral G11near the center and second end, and tubings GG and GF, without packers,are installed from surface via access well G2 into lateral G21 withthere ends near its center and second end. Mining can be initiated byinjection or recovery of solvent from the shoe of access well G1, theshoe of access well G2, the lower end of tubing GD, the lower end oftubing GE, the lower end of tubing GG and/or the lower end of tubing GF.In cases where the injection fluid is at a higher temperature than therecovery fluid temperature and heat exchange is a concern, a preferredmining method is that an access well and all tubing within that accesswell be used either for injection or for recovery fluids. Lateralborehole segments between potential injection/recovery points canproceed either sequentially, or simultaneously.

In FIG. 8, a dual access well system is shown for mining a beddedevaporite mineral resource with multiple lateral boreholes. The view ofthe FIG. 8 could be an overhead view relative to the ground surface or aside view depending on the resource to be mined and the mine plan. Dualaccess wells H1 and H2 are drilled to access an evaporite mineralformation. They are then cased, cemented and bonded to the walls of theboreholes. For one scenario, the access wells are drilled downvertically to the top of an evaporite formation containing bed 1, bed 2,bed 3 and bed 4 (from top to bottom). Prior to penetrating the roof ofthis bedded evaporite mineral resource, the drill is stopped and pulledout to allow casing HA and HB to be installed in the boreholes fromslightly above the surface (not shown) to the end of the wellbores asshown. The casings are then cemented and bonded to the borehole wall,preferably from the end of the drill to up to the surface. At thispoint, all the lateral boreholes that have a first connection to anaccess well are drilled preferably using a smaller diameter drillingunit and MWD tool. Lateral H11 is drilled from access well H1 to a pointHC and curved about 90 degrees to become tangent with and extend alongthe floor of bed 4 (not shown) floor a substantial distance to point HD.A second, substantially parallel lateral borehole H21 is drilled fromaccess well H2 to a point HE and curved about 90 degrees such that thelateral H21 becomes tangent with and extends along the floor of bed 4substantial distance to join lateral H11 in holy communication at pointHE. Laterals H11 and H21 can have an angle of intersect that is notevident in this two dimensional figure. Tubing HF and HG, with packers,are installed in lateral H11 and H21 to the roof of bed 4. Tubing HH andHI, without packers, are installed into their respective laterals H11and H21 below the lower end of tubings HF and HG but short of point HE.The lower ends of tuning HF, HG, HH and HI serve as injection/recoverypoints for fluids used to mine bed 4 between the lower ends of tubing HFand HG. Injection and recovery flows are reversed from time to time andtubing HH and HI are advanced and refracted or plugged and perforated toimprove bed 4 resource recovery.

When lateral H11 and H21 mining of bed 4 is compete, tubing HH and HIare pulled to the surface, a plug is set inside the packers of tubing HFand HG, tubing HF and HG are cut above the plug and pulled to surfaceallowing cement to be placed on top of the plug to a point above bed 3that allows new laterals H12 and H22 to be drilled a substantialdistance in bed 3 to join in communication at point HI. Tubing HJ and HKare installed in laterals H12 and H22 near but short of point HJ. Bed 3is solution mined by alternately injecting and recovering from tubing HJand HK. Tubing HJ and HK are advanced and retracted or plugged andperforated during the mining process to improve mining performance.

When lateral H12 and H22 mining of bed 3 is complete, tubing HJ and HKare pulled to surface and unmined curves of laterals H12 and H22 areplugged and cement is placed on the plugs. The cemented intervals extendupwards into lateral H11 and H21 to a height sufficient to allow newlaterals H13 and H23 to be drilled.

Laterals H13 and H23 connect laterals H11 and H21 without connection orcommunication by utilization of the third dimension not evident in thetwo dimension FIG. 8. In this view, lateral H13 is drilled from backsideof lateral 11 and circles around the far side of plane between lateralH11 and H21 to connect with the backside of lateral H21 at point HL.Lateral H23 is drilled the out the nearside of lateral H21 and circlesaround the near side of the plane between laterals H11 and H21 toconnect with the nearside of lateral H11 at point HM. Laterals H11 andH21 are reopened by drilling below the branch of laterals H13 and H23 tocommunicate with laterals H13 and H23 at points HL and HM. Tubing HN,without packer, is set in lateral H11 above the branch of H13 from H11.Tubing HO, without packer, is set in lateral H21 above the branch oflateral H24 from lateral H21. Tubing HP, with packer, is set below thebranch of H11 and H13 and above the connection of H23 with H11 at pointHM. Tubing HQ, with packer, is set below the branch of lateral H21 andH23 and above the connection of lateral H13 with H21 at point HL. Thelateral H13 and H23 mining in performed by injecting and recovering fromtubing HN, HO, HP and HQ such that lateral H14 and H24 can be mined insequence, series or parallel with forced flow.

One skilled in the art with knowledge of this invention may find use formore than the two access wells connected in the third dimension. Oneskilled in the art will recognize the opportunity to drill all thelaterals between H11 and H21 before mining and to use various tubing,packer, plug and perforation combinations to mine the various connectedlaterals in beds in sequence, series or in parallel and distribute theinjection and recovery point impacts and cause forced flow in alllateral boreholes in the system. One skilled in the art will see and beable to utilize opportunities to add additional vertical ordirectionally drilled access wells and primary laterals such as H11 andH21 and laterals in the third dimension including the use of spirals andmultiply curved laterals.

In another embodiment of the present invention, there is provided amethod for solution mining of an evaporite mineral, which includesdrilling at least two access wells extending into an evaporate mineralformation, drilling a first array of at least two substantially parallellateral boreholes, and drilling a second array of at least twosubstantially parallel lateral boreholes. In this embodiment, theboreholes in the first array are not parallel with the boreholes in thesecond array, and the boreholes in the first and second arrayscommunicate with at least one borehole in the other array or with anaccess well. The method further includes injecting a fluid into at leastone of the access wells, and collecting a pregnant solution containing adissolved evaporite mineral from at least one of the access wells.Optionally, the method may include drilling a third array of at leasttwo substantially parallel lateral boreholes; wherein the boreholes ineach of the arrays are not parallel with the boreholes in any otherarray; and wherein the boreholes in the first, second and third arrayscommunicate with at least one borehole in another array or with anaccess well.

FIGS. 9, 10 and 11 provide illustrations of particular embodimentsdiscussed in the preceding paragraph. In FIG. 9, a dual access wellsystem is shown for mining a bedded evaporite mineral resource withmultiple lateral boreholes. The view of the figure is an overhead viewrelative to the ground surface. Directionally drilled dual access wellsI1 and I2 are drilled to access a bed of an evaporite mineral in apreferred manner. Access wells are drilled, cased and cemented to bondthe casing to the borehole. For one scenario the access wells I1 and I2are initially drilled down vertically and then directionally drilled toturn or curve toward each other from opposing directions and terminatewith the access well borehole tangent with the floor of a nearlyhorizontal bed. The drill string (not shown) is pulled out and casingsIA and IB are installed in the boreholes from slightly above the surface(not shown) to the end of the access well borehole as shown. The casingsare then cemented and bonded to the borehole wall, preferably from theend of the drill to up to the surface. At this point, all the lateralboreholes which have a first connection to an access well are turnedapproximately 45 degrees in plan view so that the lateral boreholes aredrilled in a substantially horizontal manner relative to the groundsurface in accordance with the disposition of the bedded resource to bemined (not shown). Preferably a smaller diameter drilling unit and MWDtool are installed on the drill string and a first lateral borehole I11is drilled from access well I1 to a point IC and curved to create acurvature of approximately 45 degrees as shown. A second lateral I12 isdrilled off the backside of the lateral I11 curve to be substantiallyperpendicular to lateral I11 to point ID. Lateral I21 is then drilledfrom access well I2 along the floor of the bed to turn approximately 45degrees and extend to communicate with lateral I11 at point IC. Thedirectional drilling assembly is pulled back into the lateral I21 curveand used to extend lateral I22 off the backside of the lateral I21curve. Lateral I22 is drilled toward the shoe of access well I1 for somedistance before being turned about 45 degrees opposite the lateral I21curve and extended to communicate with lateral I12 at point ID. Thedirectional drilling assembly is pulled back into the lateral I22 curveand used to extend lateral I23 off the backside of the lateral I22curve. Lateral I23 is drilled toward the shoe of access well I1 for somedistance before being turned about 45 degrees opposite the lateral I22curve and extended substantially parallel to lateral I21 to communicatewith lateral I11 at point IE. The directional drilling assembly ispulled back into the lateral I23 curve and used to extend lateral I24off the backside of the lateral I23 curve. Lateral I24 is drilled towardthe shoe of access well I1 for some distance before being turned about45 degrees opposite the lateral I23 curve and extended substantiallyparallel to lateral I22 to communicate with lateral I21 at point IF. Thedirectional drilling assembly is pulled back into the lateral I24 curveand used to extend lateral I25 off the backside of the lateral I24curve. Lateral I25 is drilled toward the shoe of access well I1 for somedistance before being turned about 45 degrees opposite the lateral I24curve and extended substantially parallel to lateral I23 to communicatewith lateral I11 at point IG. The directional drilling assembly ispulled back into the lateral I25 curve and used to extend lateral I26off the backside of the lateral I25 curve. Lateral I26 is drilled towardthe shoe of access well I1 for some distance before being turned about45 degrees opposite the lateral I25 curve and extended substantiallyparallel to lateral I24 to communicate with lateral I21 at point IH. Thedirectional drilling assembly is pulled back into the lateral I26 curveand used to extend lateral I27 off the backside of the lateral I26curve. Lateral I27 is drilled toward the shoe of access well I1 for somedistance before being turned about 45 degrees opposite the lateral I26curve and extended to communicate with lateral I21 at point II. Thedirectional drilling assembly is pulled back into the lateral I27 curveand used to extend lateral I28 off the backside of the lateral I27curve. Lateral I28 is drilled toward the shoe of access well I1 for somedistance before being turned about 45 degrees opposite the lateral I27curve and extended substantially parallel to lateral I26 to communicatewith lateral I21 at point IJ. The directional drilling assembly ispulled back into the lateral I28 curve and used to extend lateral I29off the backside of the lateral I28 curve. Lateral I29 is drilled towardthe shoe of access well I1 for some distance before being turned about45 degrees opposite the lateral I28 curve and extended to communicatewith lateral I21 at point IK.

Tubing IL, with packer, is installed in the first end of lateral I29 andis used to inject fluids that mine I29 and a portion of I11 withrecovery is at the shoe of access well I1. Laterals I29 is mined withforced flow that can be reversed from time to time to improve miningperformance. A second tubing from surface via tubing IL can be extendedinto the lateral I29 to further distribute the injection point impacts.

When lateral I29 mining is complete, a plug is set inside the tubing ILpacker. Tubing IL is cut and pulled to the surface leaving a section ofthe IL tubing, packer and plug to seal in the mined out I29 lateral.Tubing IM, with packer, is installed in first end of lateral I28 andused to mine lateral I28 and a portion of lateral I12 in a manner tubingIL and lateral I29. This process is repeated with tubing IN, IO, IP, IQ,IR, and IS to mine laterals I27, I26, I25, I24, I23, I22 and I21respectively. In many cases, a single tubing with a series of packersusing plugs and perforations can be used to individually mine all thelateral independently with forced flow without the effort of replacingthe tubing and packer each time a lateral is mined out. One skilled inthe art with knowledge of this invention can develop alternative lateralborehole and tubing arrangements including the use of tubing and packersin lateral L11.

In FIG. 10, a dual access well system is shown for mining an evaporitemineral resource with multiple lateral boreholes. In FIG. 10, a dualaccess well system is shown for mining a bedded evaporite mineralresource with multiple lateral boreholes. The view of the figure is anoverhead view relative to the ground surface. Directionally drilled dualaccess wells J1 and J2 are drilled to access a bed of an evaporitemineral. Access wells are drilled, cased and cemented such that lateralscan be extended into the mining zone. For one scenario the access wellsJ1 and J2 are initially drilled down vertically and then directionallydrilled to turn or curve toward each other from opposing directions andterminate with the access well borehole tangent with the floor of anearly horizontal bed. The drill string (not shown) is pulled out andcasings JA and JB are installed in the boreholes from slightly above thesurface (not shown) to the end of the access well borehole as shown. Thecasings are then cemented and bonded to the borehole wall, preferablyfrom the end of the access well borehole to up to the surface. At thispoint, all the lateral boreholes which have a first connection to anaccess well are turned approximately 45 degrees in plan view so that thelateral boreholes are drilled in a substantially horizontal mannerrelative to the ground surface in accordance with the disposition of thebedded resource to be mined (not shown). Preferably a smaller diameterdrilling unit and MWD tool are installed on the drill string and a firstlateral borehole J11 is drilled from access well J1 to create acurvature of approximately 45 degrees in the plan view and extended topoint JC. A second lateral J12 is drilled off the backside of thelateral J11 curve to be substantially perpendicular to lateral J11 andextended to point JD. Lateral J13 is drilled of the backside of thelateral J12 curve and drilled toward the shoe of access well J2 somedistance where it is turned in the plan view about 45 degrees andextended to point JE. The directional drilling assembly is returned tothe J13 curve where it is used to drill lateral J14 off the backside oflateral J13 curve toward the shoe of access well J2 some distance andthen lateral J14 curves and communicates with lateral J21 at point JF.Lateral J21 is then directional drilled from access well J2 turning inplan view to create a curvature of about 45 degrees while drilling alongthe floor of the bed and is extended to communicate with lateral J14 atpoint JF and then with J13 at point JE and finally lateral J12 at pointJD. The directional drilling assembly is pulled back into the lateralJ21 curve and used to drill lateral J22 off the backside of the lateralJ21 curve. As lateral J22 is drilled along the floor of the bed, it isturned in plan view, opposite the lateral J21 curve, to be perpendicularto lateral J21 and extended to communicate with lateral J11 at point JC.The directional drilling assembly is pulled back into the lateral J22curve and used to drill lateral J23 off the backside of the lateral J22curve. Lateral I23 is drilled along the floor of the bed toward the shoeof access well J1 for some distance and then turned about 45 degrees inthe same direction as lateral J22 and extend to communicate with lateralJ11 at point JG. The directional drilling assembly is returned to theJ23 curve where it is used to drill lateral J24 off the backside oflateral J23 curve toward the shoe of access well J1 some distance andthen lateral J23 curves and communicates with lateral J11 at point JH.

Tubing JH with three packers is installed to the first end of lateralJ14 such that packer one is set in the first end of lateral J14; packertwo is set in the first end of lateral J13; and packer three is set inthe first end of lateral J12. Tubing JI, with three packers, isinstalled in lateral J24 such that packer one is set in the first end oflateral J24; packer two is set in the first end of lateral J23; andpacker three is set in the first end of lateral J22.

A potential mining method is mining lateral J14 by injecting from theopen end of tubing JH and recovery at the shoe of access well J2. Whenlateral J14 is mined out, a plug is set tubing JH packer one and tubingJH is perforated following packer two to initiate flow and mining inlateral J13 while recovering from the shoe of access well J2. Whenlateral J13 is mined out, a plug is set in tubing JH packer two andtubing JH is perforated following packer one to allow injection ofmining flows into lateral J12. When lateral J12 is mined out, injectionbegins at the open end of tubing JI into lateral J24. Similar pluggingand perforating steps are used to mine laterals J23 and J22. One skilledin the art can apply flow switching and other tubing, packer and plugand perforation arrangements and plugs can be installed and removed tofacilitate additional recovery.

In FIG. 11, a dual access well system is shown for mining a beddedevaporative resource with multiple lateral boreholes. The view of thefigure is an overhead view relative to the ground surface. Directionallydrilled dual access wells K1 and K2 are drilled to access an evaporitemineral formation. The access wells are cased, cemented, and bonded tothe walls of the boreholes. For one scenario the access well isinitially drilled down vertically and then is turned or curved to almostintercept the evaporite mineral formation near the roof line. Prior topenetrating the roof of the evaporite mineral formation, the drill isstopped. Drill string (not shown) is pulled out and casing KA and KB areinstalled in the boreholes from slightly above the surface (not shown)to the end of the well bore as shown. The casing is then cemented andbonded to the borehole wall, preferably from the end of the casing shoeto up to the surface. At this point, all the lateral boreholes whichhave a first connection to an access well are turned approximately 90degrees to the surface so that the lateral boreholes are drilled in asubstantially horizontal manner relative to the ground surface inaccordance with the disposition of the bedded resource to be mined (notshown). Preferably a smaller diameter drilling unit and MWD tool areinstalled on the drill string and a first lateral borehole K11 isdrilled along the bed floor while curved about 45 degrees from accesswell K1 to a point KC. A second lateral K12 is drilled from the backsideof the lateral K11 curve along the bed floor while curving opposite thelateral K11 curve to be substantially perpendicular to lateral K11 andextend to point KD. Additional lateral boreholes K13, K14, K15, K16,shown, are drilled in like manner to points KE, KF, KG and KHrespectively. Access well K2 laterals K21, K22, K23, K24, K25 and K26are drilled in like manner to points KC, KI, KJ, KK and KL. Accordingly,the first end of lateral borehole K11 communicates in order with accesswell K1 and the second ends of laterals K26, K25, K24, K23 and K22 atpoints KL, KK, KJ, KI and KC respectively; the first end of lateralborehole K12 communicates with the curve of lateral K11 and its secondend communicates with lateral K21 at point KD; the first end of lateralK13 communicates with the curve of lateral K12 and its second endcommunicates with the lateral K21 at point KE; the first end of lateralK14 communicates with the curve of lateral K13 and its second endcommunicates with lateral K21 at point KF. in order with access well andlaterals; the first end of lateral K15 communicates with the curve oflateral K14 and its second end communicates with lateral K21 at point KGand the first end of lateral K16 communicates with the curve of lateralK15 and its second end communicates with lateral K21 at point KH. Accesswell K2 laterals K21, K22, K23, K24, K25 and K26 communicate in a likemanner as shown. Tubing, packers, plugs and perforations can be used aspreviously described to mine each lateral with forced flow. Access wellshoes and tubing (not shown) may be used to inject or recover miningfluids at various points in the lateral system. Mining can progresseither from one lateral to another sequentially, or simultaneously amongall of the boreholes. Tubing, tubing packers and plugs can be used todistribute the injection and recovery point impacts and cause forcedflow in all lateral boreholes in the system.

In FIG. 13, a dual access well system is shown for mining a beddedevaporative resource with multiple lateral boreholes. The view of thefigure is an overhead or side view relative to the ground surface.Directionally drilled dual access wells M1 and M2 are drilled to accessan evaporite mineral formation. The access wells are cased and cementedto bond the casing to the walls of the boreholes. For one scenario theaccess well is initially drilled down vertically and then is turned orcurved to intercept the evaporite mineral formation. When the accesswell borehole is tangent with the floor of the bed, drilling is stopped.The drilling assembly is pulled out and casing is installed in theboreholes from slightly above the surface (not shown) to the end of thewell bore as shown. The casing is then cemented and bonded to theborehole wall, preferably from the end of the casing shoe to up to thesurface. At this point, the laterals M11 and M21 that have a firstconnection to an access well are drilled along the floor of the bedtoward the opposing access well some distance and then turned oppositedirections about 45 degrees and extended to point ML and MKrespectively. A second lateral M12 is drilled from the backside of thelateral M11 curve and is extended along the bed floor while curvingopposite the lateral M11 curve to be substantially perpendicular tolateral M11 and extend to connect in communication with lateral M21 atpoint MK. Lateral M22 is drilled off the backside of the lateral M21curve along the floor of the bed to become substantial perpendicular tolateral M21 and is extended to connect in communication with lateral M11at point ML. Tubing MA, with packer, is installed just before thelateral M11 and M12 branch. Tubing MB, with packer, is installed in thecurve of lateral M12. Tubing MC and MD, with packers, are installed insimilar manner as shown. Mining can progress injecting and recoveringfrom the open ends of tubing MA, MB, MC and MD until laterals M11, M12,M21 and M22 are mined out. At that pint tubing MB and MC are cut abovethe packers and pulled from the wells. A plug is set in the packers oftubing MA and MD, before they are cut and pulled from the wells.Laterals are drilled and mined using tubing ME, MF, MG and MH in likemanner. When laterals M13, M23, M14 and M24 are mined out, there relatedtubing is plugged removed as previously described and laterals M15, M16,M25 and M26 are drilled. Tubing MI, with packer is installed fromsurface and is set in the lateral M16 curve. Tubing MJ, with packer, isinstalled from surface and is set in the curve of lateral M26. LateralsM15, M16, M25 and M26 are mined with injection and recovery from theshoes of the access wells M1 and M2 and the open ends of tubing MI andMJ. Any number of substantially square or rectangle or round sets oflaterals can be completed and mined in his manner, including thosebeginning from windows milled in the cased and cemented access wells M1and M2. The substantially square, rectangle or round sets of lateralsneed not be in the same plane as shown on the two dimensional figure.The tubing, packer and plug arrangement shown provides a forced measuredflow to mine each lateral. One skilled in the art with knowledge of thisinvention can reduce or expand the tubing, packer and plug arrangement.

The present invention also includes method for solution mining of anevaporite mineral which includes drilling at least one access wellaccessing an evaporate mineral formation and drilling a first and secondlateral boreholes. The two lateral boreholes communicate with each otherand at least one of the lateral boreholes is connected to the at leastone access well. The method further includes injecting a fluid into theat least one access well and circulating the fluid through the firstlateral borehole to produce a first pregnant solution containing adissolved evaporite mineral to produce a first cavity, and collectingthe second pregnant solution. The method further includes circulatingthe fluid through the second lateral borehole to produce a secondpregnant solution containing a dissolved evaporite mineral to produce asecond cavity and collecting the pregnant solution. In a preferredembodiment, the method further includes circulating the fluid throughthe second lateral borehole after said step of circulating the fluidthrough the first lateral borehole, and said first lateral borehole isbelow said second lateral borehole. In another preferred embodiment, thebarrier that exists between the first cavity and the second lateralborehole collapses and such collapse opens a communication between thefirst cavity and the second borehole.

One example of use of sequential mining utilizing a natural barrier tofavorably influence solution mining is a trona resource with a 5-footlower bed, and 25-foot upper bed and a separating 7-foot shale layer.The lower 5-foot bed may be solution mined first from a lateral boreholeplaced within that bed. The 7-foot shale natural barrier halts upwardleaching causing the mining solutions to more actively leach the wallsto widen the cavity within the 5-foot bed. Such a method improves therecovery from the 5 foot lower bed and widens the cavity in the 5-footbed to undercuts the 7 foot barrier and eventually causing it to fail.Failure can be either an advancing rubblization of the shale or failureas a structural beam. The 25-foot upper bed may fail at the same time asthe 7-foot barrier or may stay in place for a period of time. Eitherway, introduction of the ore in the 25-foot bed to the top of theactively mined cavity occurs in such a manner such that nearly 100%recovery is possible at least for the full width of the cavity in the5-foot bed. If a mine plan calls for failure of the 7-foot barrier at aspecific point in the mining process, cycling the cavity pressure and/orheating the barrier can stimulate failure. Accordingly, to mine such aresource, the at least two lateral boreholes may be disposedsubstantially vertically with respect to each other, and the lowestlateral borehole may be substantially completely solution mined beforean upper lateral borehole is substantially completely solution mined.Plugs may be disposed within at least one lateral borehole to allowsequential mining of the boreholes.

In another embodiment of the invention, the present invention alsoprovides a method for solution mining of an ore mineral formation, whichincludes drilling at least one access well accessing the ore mineralformation and drilling at least two lateral boreholes, each containing afirst end connected to the access well and a second end not in boreholecommunication with the access well or another lateral borehole. Themethod further includes injecting a fluid into an access well causingfluid flow within said ore mineral formation and collecting a pregnantsolution containing a recovered ore mineral from at least one lateralborehole. The lateral boreholes communicate on a first end with eitheran access well or a lateral borehole, but on a second end, the lateralboreholes are in fluid communication only through fluid flow that haspermeated through the solid rock matrix containing the ore mineral.There are no direct borehole connections between the second ends of eachlateral borehole and any other borehole.

The ore mineral formation includes a permeable rock which includes theore mineral, such as, for example, a permeable sandstone resourcecontaining uranium minerals. A preferred ore mineral to collect orrecover contains uranium. Preferably, at least a portion of the at leasttwo lateral boreholes are substantially parallel to each other. Inanother preferred embodiment, at least a portion of the lateralboreholes and the at least one access well are substantially parallel toeach other, i.e., are positioned in the same axial orientation as eachother.

In another preferred embodiment, at least a portion of the lateralboreholes and the at least one access well are drilled so that asubstantial portion of the boreholes are substantially perpendicularwith respect to the ground surface.

FIG. 12 illustrates a dual access well solution mining system forevaporate resources using with lateral boreholes which may be mined in asuccessive fashion. The view of the figure is a plan view relative tothe ground surface. The dual access wells L1 and L2 are drilled toaccess an evaporite mineral formation. Access wells are cased andcemented to bond the casing to the borehole. For one scenario a pair ofthe access wells are initially drilled down vertically and then turnedor curved by directional drilling to intercept the evaporite mineralformation and become tangent at point LA and LB with the floor of a bedselected for solution mining. Drilling of the access well boreholescontinue along the bed floor for a substantial distance beingsubstantially parallel to each other. The drill string and directionaldrilling assembly (not shown) is pulled out and casing is installed fromslightly above surface to near the end of the boreholes extended alongthe floor of the selected bed and as shown. The casing is then cementedand bonded to the borehole wall, preferably from the end of the drill toup to the surface. Preferably a smaller diameter drilling unit and MWDtool are installed on the drill string and a first lateral borehole L11is drilled from the shoe of the access well L1 and is curved at about a45 degree angle from an extended centerline of the access well andextended along the floor of the bed to a point LC that is about halfwaybetween the pair of access well L1 and L2. The directional drillingassembly is retracted to the first end of lateral L11 and used to drilllateral L12 off the backside of the lateral L1 curve. Lateral L12 iscurved as shown about 45 degrees from the extended centerline of accesswell L1 in the opposite direction as lateral L11 and extended along thefloor of the bed a substantial distance to point a LD. The length of allthe lateral boreholes in this Figure is approximately 1750 feet. TubingLE is installed from slightly above surface to near point LD at thesecond end of lateral L12. Lateral L21 is now drilled from the shoe ofaccess well L2 turning about 45 degrees from the extended centerline ofthe access well and extended along the floor of the bed to communicatewith lateral L11 at point LC. The drill is returned to the shoe ofaccess well L2 and a lateral L22 is drilled off the backside of thelateral L21 curve to turn about 45 degrees relative to the extendedcenterline of the access well and extend along the floor of the bed topoint LE. Tubing LG is installed from slightly above surface to near theend of lateral L22 at point LE. Solution mining may commence at thispoint by injecting and recovering from the shoes of access wells L1 andL2 and from the ends of tubing LE and LG and using flow reversal as wellas tubing relocation, plugging and perforating to improve miningperformance. When lateral L11, L12, L21 and L22 lateral mining iscomplete, a plug is set in the access well L1 casing near its shoe andthe well is prepared for drilling the next set of laterals for miningcutting a window in the access well casing about 300 feet back from theplugged end. Preferably the plug is drillable. From this window,laterals are drilled and mined in a manner similar to the first set L11,L12, L21 and L22. This retreat drilling and mining process can berepeated many times. Tubing and tubing packers can be used to distributethe injection and recovery point impacts and cause forced flow in alllateral boreholes in the system. Where mining benefits from moreinjection and recovery point in the laterals being mined, commonly usedtechniques can be used to place more than one tubing into the lateralsL12 and L22. Less common but available techniques can also be used togain tubing access to the laterals L11 and L21 in addition to lateralsL12 and L22. In the access well, tubing to the first drilled lateralsL11 or L21 would parallel the tubing that extends to the second drilledlaterals L12 or L22. The techniques used to drill multiple laterals fromthe shoe of an access well in a manner that allows placement of tubingin each lateral is an example of emerging drilling and completiontechniques and practices that one skilled in the art can adapt toenhance the efficacy of the invention.

In another embodiment of the present invention, a method of constructingan underground configuration is provided. This method includes drillingat least one access well and drilling at least two lateral boreholes. Atleast two lateral boreholes communicate with each other and at least oneof the lateral boreholes is connected to the access well. Such anunderground configuration allows for substantially equal or controlledfluid flow throughout the lateral boreholes, and will have manynon-solution mining applications. A few embodiments of non-solutionmining are described below, but more will occur to those of skill in theart.

In one preferred embodiment, the underground configuration is a waterwell providing improved access and flow from an underground watersource. Methods known in the art for water well drilling may be used inconjunction with this method.

In another preferred embodiment of an underground configuration, theunderground configuration is used for mining an evaporite ore mine, oilshale mine, a tar sand mine, and a coal mine. In the case of oil shale,there have been numerous failures to economically mine oil shale. Anumber of preexisting methods of mining oil shale, such as the methodstaught by U.S. Pat. No. 3,967,853, which is incorporated by referenceherein in its entirety, are compatible with methods of constructing anunderground configuration. Such methods include in situ production usinghot fluid-induced pyrolysis or thermo or anaerobic microorganismconversion of the organic solids to fluids. Similarly, this inventionmay be used in conjunction with known methods of mining and recoveringfrom tar sands or from coal mines.

In another preferred embodiment, the underground configuration of thepresent invention may be used to clean and/or contain threateningsubterranean fluids such as toxic chemical plumes adjacent tounderground aquifers.

In another preferred embodiment, the underground configuration of thepresent invention may be used for subterranean storage and/or disposalof materials. An underground configuration may be adapted to increasethe volume of space available for storage and/or disposal relative to agiven amount of underground area, relative to presently knownsubterranean storage configurations. Drilling and the number of lateralboreholes drilled are adapted in light of the ability of the undergroundformation to support multiple boreholes without danger of subsidence orcollapse. Preferred substances to store and/or dispose include gasessuch as natural gas and liquids such as coal bed methane productionwaste waters.

The following example is provided for the purpose of illustration and isnot intended to limit the scope of the present invention.

Example 1

The following describes an application of this invention to mineWyoming's Green River Basin trona and produce various sodium products.All depths are from surface. All temperatures and concentrations are“about” that provided in the discussion. The resource is defined asbarren from the land surface down to the top of Bed 17 at a depth of1543-ft. Moving downward from the top of Bed 17 the trona rich beds thatare less than 2% salt are characterized as: (11′ Bed 17) (42′ barrier)(3′ Bed 16) (6′ barrier) (5′ Bed 15) (42′ barrier) (138′ intermingledbedded mixed trona and salt and barriers) (4′ barrier) (5′ Bed 7) (7′barrier) (8′ Bed 6) (6′ barrier) (9′ Bed 5) (23′ barrier) (10′ Bed 4)(9′ barrier 3) (7′ Bed 3) (19′ barrier) (13′ Bed 2) (15′ barrier) and(3′ Bed 1). The beds dip deeper to the north at a rate of 2′ per 100′.The in situ temperature at 2,000-foot depth is 95° F. In thisevaluation, production of 95 lbs of salable sodium sesquicarbonate(recrystallized trona) per cubic foot of trona bed consumed by thesolution mining process is estimated. Included in this estimate is notproducing 10% of the trona dissolved as it remains dissolved in themassive amount of mining fluid remaining in the mined out cavity.Recovery of 105 lbs of salable sodium sesquicarbonate can be achieved byrecovering and processing this final cavity solution.

A novel plan to improve resource recovery, conserve water and gainadditional economic value from a cavity is pushing the final cavitysolution out of the cavities with compressed natural gas in the summeras an initial phase of a natural gas storage project. Fresh water couldbe used to push the natural gas out of the cavity as desired during thehigher value peak demand season. Given the long dissolution period, thesolutions produced during the gas storage phase would saturate eachcycle. Allowance for this additional cavity growth is an importantnatural gas storage project design. Presaturated solution could be usedto control the additional cavity growth if desired.

Retired cavities are also used to pre-treat the raw water entering thesodium production facilities. Passing the raw makeup water though an oldcavity would clarify the raw water, eliminate the Ca and Mg ions bycarbonate precipitation and increase the productivity of the facilitiesby pre-saturating the process make-up water. The vast amount of solutionstored in the cavity would act as a secure water supply in much the sameway as a surface reservoir.

This trona resource will be mined in this example using the dual wellmethod as shown by FIG. 12. All casing sizes are approximate. A pair of1,000′ deep vertical 14″ cased and cemented access wells, L1 and L2, arespaced East-West a distance of 2,500′. Laterals LA and LB are thendirectionally drilled curving toward the north from each of the twoaccess wells L1 and L2 to become tangent with and run for 1,120′ justabove the base of Bed 15. A 12″ casing is run to the bottom (far end) ofLA and LB boreholes and cemented in place continuously along the 1,120′length on the floor of Bed 15 and several hundred feet upward into thelower portion of the curve. The 12″ casing is set in the well head undertension such that no slack can occur when heated to 300° F. Tubingpackers in the 12″ casing system can replace some or all the cement toallow more flexible and lower cost recompletion as mining advancescavity to cavity using this well pair.

From the lower end of LA and LB, directionally drill laterals L11 andL21 along the floor of Bed 15 while building 45° of angle toward eachother and then extend each to the half way point between the two wellsso that they hydraulically intersect at the mid-point. Jet washing orfracing can assist gaining hydraulic connection if necessary. From LAand LB drill second laterals L12 and L22 in a similar manner as thefirst directional laterals but in the opposite direction, and extendeach a distance of 1800 feet. Complete these opposing laterals byrunning a 8″ tubing to the end of L12 and L22 Equip each of thewellheads with automated flow control valves, sample ports, andinstrument package (flow rate, temperature, specific gravity andpressure) such that each of the 8″ tubings and 12″ casings can be usedto inject or recovery solutions. In this the hot solution miningexample, the heat exchange potential of the tubing and casing is suchthat simultaneous same well injection and recovery is avoided.

Mining is initiated with ambient temperature water followed by about 90°C. solvent containing about 8% by weight soda ash to avoid secondaryprecipitation of Wegscheiderite or nahcolite. Injection and recovery isalternated between well LA and LB at about 2 day intervals or anytimeflow restriction is noted. Operate in this manner to build an insolubledebris pile covering each injection/recovery point forming theequivalent of a water well gravel pack. This phase is complete whenrecovery and resource based calculations indicate several feet ofinsoluble rubble has formed at each of the injection/recovery points.The flow rate during this period is about 500 gallons per minute.

Commercial operation is initiated by switching to water injection andramping up the flow rate and temperature to 2,000-gpm and a recoverytemperature about 5° C. above the TWA point. The TWA temperature anddissolved solid concentrations shown in FIG. 14 are not exact and canshift with impurities concentrations. One skilled in the art can betteridentify the TWA point in the lab and by determining the temperature ofmaximum concentration of dissolved solids in the recovered solutionswhen operating nearly saturated along the trona—Wegscheiderite solidphase boundary. Above the TWA temperature, increased temperature willdecrease the solution concentration of solid materials. Below the TWAtemperature, deceased temperature will also decrease the solutionconcentration of solid materials. The TWA point should be approachedfrom the high temperature side so that cooling of the solutions intransport to the plant are less likely to cause super saturation andpotential precipitation plugging of the recovery well and pipeline.

Initially, solution mining is contained in the 5′ thick Bed 15. Whenflow, temperature and concentration have stabilized for a few weeks,reverse the flows at the wellheads and sample and assay the freshlyreturning recovery flows during the transition period to gain the dataneeded to estimate the relative leach rate for various sections of thecavity. Using the relative leach rate data, allocate production to eachcavity section and estimate the cavity production and profile in eachsection. Based on data and calculations, adjust the injection andrecovery flow rates and switch injection and recovery flow directions ina manner designed to balance the recovery in the 7,000 feet of boreholein this cavity.

To the extent possible, use steady pressures and temperatures to mine asmuch as possible from Bed 15 before the failure of the its 6′ roof thatintroduces Bed 16 to the expanding cavity. In a similar way, mine thecombined Bed 15 and 16 system until the 42′ Bed 16 roof failsintroducing Bed 17 to the expanding cavity. The mining process continueswith Beds 15, 16 and 17 actively combined in single mining cavity. Thecombined trona bed thickness of bed 15, bed 16, and bed 17 noted aboveis 19-feet. The total mining borehole length of lateral L11, L12, L21and L22 is about 7000-feet without including the several hundred feet ofrounding that mining adds to the cavity length. When an effectiveaverage cavity width of 200-feet is achieved, 27-million cubic feet ofore has been mined (7000′ by 200′ by 19′). At 95-pounds of tronaproduction per cubic foot of trona ore mined means that the initialborehole L11, L12, L21 and L22 yield from the Bed 15, 16 and 17 mininginterval produced 1.3 million tons of sesquicarbonate (recrystallizedtrona) on surface without harvesting a final solution Mining willcontinue as long as economic heat loss and solution concentrationscontinue and subsidence potential is acceptable. For this example, thiscavity is shut in at this point and mining advances to the next cavityby recompleting the wells.

When initial (lateral L11, L12, L21 and L22) bed 15, 16 and 17 cavitymining is complete, the 8-inch tubing is recovered and the 12″ casing isplugged near the shoe. Then a window is milled about 600-feet back fromthe shoe and a new set of interconnected and opposing laterals aredrilled, completed and mined. FIG. 12 notes these as laterals L13, L14,L23 and L24. FIG. 12 shows two such pullback cycles and three cavitiesmined by this set of access wells. More are possible if spaced closureor the 12′ casing were extended a greater distance along the floor ofBed 15. If all three cavities were shut in at a 200-ft effective width,the combined production from the three cavities in bed 15, 16 and 17mining interval is about 4-million tons.

When the Bed 15, 16 and 17 mining with this set of wells is complete,the 12-inch casing is plugged and severed at the top of its cementedinterval. The 12-inch casing is recovered from the well and the openhole below the 14-inch casing shoe is cemented. This allows a seconddrilling and mining phase to produce the bed 1, 2, 3, 4, 5, 6 and 7mining interval in the same manner as the overhead interval Bed 15, 16and 17.

The combined trona bed thickness of this lower mining interval is55-feet or 2.9 times that of the 19-feet combined bed thickness of theupper mining interval. The mining potential of the lower interval is atleast 3 times that of the upper or nearly 12-million tons. However, ifthe mine plan requires salt avoidance, mining may be terminated whenroof falls expose the overhead salt above Bed 7. The volume of solventfilling the mined cavity is large and can accept large volumes of saltbefore becoming too salty. Should salt concerns eliminate mining of thetop 3 beds of the 7 beds lower mining interval, its potential is reducedfrom 12 to 7 million tons.

If 4,000,000-tons were recovered from the three cavity upper mininginterval and 7,000,000 to 12,000,000 tons are recovered from the lowermining interval the total recovery of this well pair is 11 to 16 milliontons of trona produced on surface assuming the ore is 90% pure andwithout harvesting the 10% of the possible production contained in thefinal shut-in cavity solution.

Salt need not terminate mining. Significant soda ash is dissolved evenin salt saturated aqueous solutions. Sufficient hydroxide (OH) can beadded to the injected solvent to chemically convert the bicarbonate tosoda ash at the point of dissolution resulting in salt brine that isrich in soda ash. The soda ash can be produced with or withoutco-producing salt using known processes. Other known processes avoid theuse of hydroxide. For example, salt saturated solutions will dissolvetrona while subsequently precipitating excess sodium bicarbonate in thecavity to provide a soda ash rich production solution Mine plans that donot require salt avoidance can skip mining the upper interval andinitiate solution mining in Bed 1 and progressively mine all overheadbeds without significant additional drilling or recompletion. Such asalty mine plan simplifies and lowers the cost of drilling and miningand allows lower temperature cavity operation at the expense of greaterflow rates to achieve the same productivity.

In this example, the solution mine product is sodium sesquicarbonate andsoda ash produced by the monohydrate process. The recovered solution isfirst cooled and evaporated to produce salable sodium sesquicarbonatewhich is in part converted and sold as light soda ash. The solutionrecovered from the sodium sesquicarbonate process feeds a monohydrateplant producing salable soda ash. The solution recovered from themonohydrate process is hot and ready to return to the mining cavity withminor additional heating.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. Althoughthe description of the invention has included description of one or moreembodiments and certain variations and modifications, other variationsand modifications are within the scope of the invention, e.g., as may bewithin the skill and knowledge of those in the art, after understandingthe present disclosure. It is intended to obtain rights which includealternative embodiments to the extent permitted, including alternate,interchangeable and/or equivalent structures, functions, ranges or stepsto those claimed, whether or not such alternate, interchangeable and/orequivalent structures, functions, ranges or steps are disclosed herein,and without intending to publicly dedicate any patentable subjectmatter.

We claim:
 1. A method of constructing an underground configurationcomprising: a) drilling at least one access well; and b) drilling atleast two lateral boreholes, wherein the at least two lateral boreholesare directly communicating with each other and wherein at least one ofthe lateral boreholes is connected to the at least one access well;wherein construction of said underground configuration allows for andfacilitates the management of fluid flow in the lateral boreholes,wherein controlled measurable fluid flow is maintained through thelateral boreholes by the use of components or methods selected from thegroup consisting of inlet fluid pressure, packers, plugs, casing,cement, perforations, specific gravity gradients, artificial leachbarriers, natural intrabed barriers, natural interbed barriers, flowreversal, adjustable tubing controlled injection, adjustable tubingcontrolled recovery points and combinations thereof.
 2. The method ofclaim 1, wherein the underground configuration is a water well.
 3. Themethod of claim 1, wherein the underground configuration is selectedfrom the group consisting of an evaporite ore mine, oil shale mine, atar sand mine, and a coal mine.
 4. The method of claim 1, wherein theunderground configuration is a containment barrier for undergroundcontaminants.
 5. The method of claim 1, wherein the undergroundconfiguration is a subterranean storage facility.
 6. The method of claim5, wherein the subterranean storage facility is for a gas.
 7. The methodof claim 6, wherein the gas is natural gas.
 8. The method of claim 5,wherein the subterranean storage facility is for a liquid.
 9. The methodof claim 1, wherein the underground configuration is an evaporite oremine.